Three Issues About Global Warming
Today, mainstream scientists recognize global warming as a challenge for our civilization, while skepticism persists. There are various types of skepticism, but we can classify them into three categories: skepticism about the trend of global warming, its anthropogenic causes, and the assessments of its impacts. Here, I would like to examine these three issues about global warming: facts, causes, and assessments. I will then consider how we should deal with global warming.
1. The Current Climate Change
Meteorologists have discussed whether the current trend of temperature is warming or cooling and whether the current climate is normal or not. In this chapter, I will examine opposing opinions about the status quo of climate among meteorologists.
1.1. The Discovery of Global Warming
Although scientists today express alarm about global warming, they were worried about global cooling until the 1970s. For example, Time Magazine predicted “the coming ice age" in 1974, and Newsweek Magazine wrote the following article entitled “The Cooling World" in 1975.
The central fact is that after three quarters of a century of extraordinarily mild conditions, the earth’s climate seems to be cooling down. Meteorologists disagree about the cause and extent of the cooling trend, as well as over its specific impact on local weather conditions. But they are almost unanimous in the view that the trend will reduce agricultural productivity for the rest of the century. If the climatic change is as profound as some of the pessimists fear, the resulting famines could be catastrophic.
Their understanding of the status quo of temperature trends was not wrong. The graph below shows the global temperature had been dropping from 1940 till 1976. Cooling was especially prominent in the Northern Hemisphere.
Why did the earth’s climate cool down then? IPCC’s Fourth Assessment Report told us an explanation by scientists at that time.
In the peer-reviewed literature, a paper by Bryson and Dittberner (1976) reported that increases in carbon dioxide (CO2) should be associated with a decrease in global temperatures. When challenged by Woronko (1977), Bryson and Dittberner (1977) explained that the cooling projected by their model was due to aerosols (small particles in the atmosphere) produced by the same combustion that caused the increase in CO2.
Joseph Fourier had already discovered the greenhouse effect in 1824. It is surprising there should be scientists that tried to associate the increases in carbon dioxide with a decrease in global temperatures in 1976. Actually, it was aerosols that brought about the cooling.
The industrialized area in the Northern Hemisphere increased sulfur dioxide emissions and tropospheric sulfate aerosol loading. Data from ice cores of Antarctica show that sulfate aerosols in the Southern Hemisphere, which is remote from anthropogenic sulfur dioxide sources, did not increase beyond normal fluctuations unlike those in the Northern Hemisphere.
Aerosols have high scattering albedo (reflectivity). They shut down solar radiation and cool down the surface temperature of the Earth. They can also be cloud condensation nuclei about which cloud droplets coalesce. Because a cloud has a high albedo, aerosols indirectly as well as directly increase the albedo of the Earth.
In recent years, sulfur dioxide emissions have decreased drastically. The clean-air laws in the industrialized area and the usage of oil instead of coal or natural gas instead of oil had the effect of reducing aerosol emissions. Today the advanced countries have regained a clear beautiful sky. Ironically resolving the air pollution problem resulted in another problem, global warming.
Should we allow air pollution to prevent global warming? Of course, we shouldn’t. Besides the health problems that it causes, the cooling that it causes is also undesirable. We should distinguish good cooling from bad cooling and good warming from bad warming. I will explain this distinction at the end of this page.
In the 1980s, the surface temperature of the Earth rose and climatologists became confused. Gradually climatologists built a consensus on global warming due to the greenhouse effect. In 1985, the Villach conference first publicly declared the consensus among them. In 1988, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) established The Intergovernmental Panel on Climate Change (IPCC), for climatologists to evaluate the risk of climate change. IPCC has published assessment reports four times and succeeded in arousing public opinion against global warming.
1.2. The Fact of Global Warming
Although climatologists today are building a consensus on global warming, some scientists are skeptical about it. The skeptics doubt whether the climate is really warming or not, whether the climate change (if it is warming) is anthropogenic or not, and whether the warming is bad for humans or not. I will take up the first skepticism in this section, the second in the next section, and the third in the third section.
As for the fact of global warming, Timothy F. Ball, former Professor of Geography, University of Winnipeg said,
The argument is that there has been warming since then  but, in fact, almost all of that is due to what is called the “urban heat island" effect – that is, that the weather stations are around the edge of cities and the cities expanded out and distorted the record. When you look at rural stations – if you look at the Antarctic, for example – the South Pole shows cooling since 1957 and the satellite data which has been up since 1978 shows a slight cooling trend as well.Frontier Centre for Public Policy (2004) Dr. Tim Ball, Historical Climatologist (Interview).</ref>
Some other scientists also claimed that the satellite data showed a cooling trend.
Unlike the surface-based temperatures, global temperature measurements of the Earth’s lower atmosphere obtained from satellites reveal no definitive warming trend over the past two decades. The slight trend that is in the data actually appears to be downward.
Is the trend of lower atmosphere really downward? Look at the graph below. It represents satellite temperature anomalies measurement of the lower troposphere, a region from the surface to about 5 miles into the atmosphere. The regression line for anomalies indicates a warming trend, though it is a gentle slope.
John Christy said at a 1997 hearing before the Senate Committee on Environment and Public Works,
It does show a slight warming trend of .06 degree per decade. It’s small enough to be easily placed within the bounds of natural variability, but I can’t be certain about that. Humans may be having a slight impact on the global tropospheric temperature.
Later he found the climate trend shown by the UAH satellite data was getting steeper.
The trend is still not as steep as that of the surface temperature of the Earth. The result of satellite measurement by RSS (Remote Sensing Systems) shows a more warming trend of the lower troposphere, whereas the stratosphere has cooled.
The IPCC fourth report assesses global warming of the troposphere at 0.04°C to 0.20°C per decade for the period 1979 to 2004, while the stratosphere has cooled at -0.32℃ to -0.47℃. This reversal resulted from the increase in greenhouse gases and the decrease in ozone. Carbon dioxide and other greenhouse gases warm the troposphere and cool the stratosphere by absorbing some of the infrared radiation emitted from the earth’s surface. Ozone absorbs solar ultraviolet radiation and emits its energy as infrared radiation, thereby warming the stratosphere.
The ozone layer was depleted as a result of the release of ozone-depleting substances into the atmosphere, such as chlorofluorocarbons (CFCs) and halons. The depletion of ozone, along with the increase in greenhouse gases, caused the temperature in the stratosphere to drop.
Timothy F. Ball ascribed the rise in surface temperature to the urban heat island effect, but according to David E. Parker, “globally, temperatures over land have risen as much on windy nights as on calm nights, indicating that the observed overall warming is not a consequence of urban development."
1.3. The Abnormality of Global Warming
The warming trend of the troposphere since the 1980s is undeniable. The next question is whether the present temperature and the current warming rate are abnormally high or not.
The IPCC Fourth Assessment Report said “Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years." It means that the Medieval Warm Period was not as warm as the Modern Warm Period.
It is, however, doubtful whether the Modern Warm Period is warmer than the Holocene Climate Optimum and it is likely that the warmest peak of the Eemian interglacial era, the previous interglacial, was warmer than that of the current interglacial era. In the Cretaceous Period, when dinosaurs thrived, it was far warmer than today and there was no ice at the poles. From a geological point of view, the Modern Warm Period is not warm. We are still living in the Ice Age, which is exceptional in the history of the Earth.
How about the warming speed, then? According to the Fourth Assessment Record, the linear warming trend over the last 100 years (1906 to 2005) is 0.74°C, and that over the last 50 years is nearly twice that for the last 100 years. Is this trend abnormal?
The largest temperature changes of the past million years are the glacial cycles, during which the global mean temperature changed by 4°C to 7°C between ice ages and warm interglacial periods (local changes were much larger, for example near the continental ice sheets). However, the data indicate that global warming at the end of an ice age was a gradual process taking about 5,000 years […]. It is thus clear that the current rate of global climate change is much more rapid and very unusual in the context of past changes.
The data of the Greenland ice core does not indicate the gradual smooth warming process. The warming process included ups and downs. When the Younger Dryas ended, it warmed by around 8°C over 40 years. Of course, it was a local change and we cannot know the global mean temperature change, but anyway it is not clear at all “that the current rate of global climate change is much more rapid and very unusual in the context of past changes."
Neither temperature itself nor the rate of temperature change is abnormal. Where does the problem of global warming lie, then? To know the nature of climate change, we must inquire into its cause.
2. The Causes of Global Warming
Today very few scientists doubt the fact of global warming, but not a few scientists doubt if the cause of the current global warming is really man-made. In this chapter, I will analyze the cause of global warming.
2.1. The Greenhouse Effect in Dispute
Whether the current global warming is natural or anthropogenic is the most important point at issue to refute skepticism. More concretely described, the problem is whether the cause is an anthropogenic greenhouse gas or the sun.
Greenhouse gases such as water vapor, carbon dioxide, methane, nitric oxide, and so on trap long-wave radiation that the Earth’s surface should radiate to space, thus raising the temperature of the troposphere. It is a well-known mechanism, but is it the only cause of global warming?
IPCC introduced the concept of radiative forcing (the change in the net, downward minus upward, irradiance at the tropopause, expressed in units of Watts per square meter) to measure the contribution of each factor to climate change.
According to the 4th Assessment Report, the RF (radiative forcing) of solar irradiance between 1750 and 2005 ranges between +0.06 and +0.3 Wm-2. On the other hand, the combined anthropogenic RF ranges between +0.6 and +2.4 Wm-2, “indicating that, since 1750, it is extremely likely that humans have exerted a substantial warming influence on climate. This RF estimate is likely to be at least five times greater than that due to solar irradiance changes.“
The 4th Assessment Report underestimates the influence of solar activity because it takes into consideration only direct forcing by changes in total solar irradiance and indirect effects of ultraviolet radiation on the stratosphere and neglects the indirect effects induced by galactic cosmic rays.
The 4th Assessment Report does not support the hypothesis of Svensmark and Friis-Christensen, which I have already introduced. But IPCC scientists do not have an alternative convincing explanation of cloud cover change. Therefore, they acknowledge scientific understanding of solar irradiance and cloud albedo effect as low, while they estimate that of the greenhouse effect to be high.
The cloud cover change, however, is not a negligible variable for the assessment of total radiative forcing.
Clouds, which cover about 60% of the Earth’s surface, are responsible for up to two thirds of the planetary albedo, which is about 30%. An albedo decrease of only 1%, bringing the Earth’s albedo from 30% to 29%, would cause an increase in the black-body radiative equilibrium temperature of about 1°C, a highly significant value, roughly equivalent to the direct radiative effect of a doubling of the atmospheric CO2 concentration.
If the solar activity can influence cloud cover and, therefore, the cloud albedo effect, it should have a high correlation with global temperature. It is well known that atmospheric CO2 concentrations have a high correlation with global temperature.
This high correlation does not demonstrate that the cause of global warming is the rise in atmospheric CO2 concentrations. The rise in temperature reduces solubility of CO2 in the ocean and raises atmospheric CO2 concentrations. We cannot know which is the cause and which is the result.
The relation between solar activity and global temperature is free from this problem. Because the Sun is far larger than the Earth, the Earth can hardly influence the Sun, though the Sun can influence the Earth. We can infer solar activity from sunspot numbers. So, first, let’s look at the relation between sunspot numbers and temperature change.
Their relationship is not clear. The graph below depicts the 11-year moving averages of the graph above.
Both lines seem to be similar until 1940. Between 1940 and 1970 sunspot numbers soar up and fall, while temperature declines a little. Aerosol must have reduced temperature in spite of high solar activity during this period. Both lines branch away after 1990. It means the solar activity cannot account for the warming after 1990.
Skeptics might think the recent rise in surface temperature is due to the urban heat island effect. Let’s examine, then, the relation between the sunspot numbers and the temperature of the lower troposphere, which is unlikely to be affected by the urban heat island effect.
Again two trends diverged after 1990. Sunspot numbers are going down but the temperature of the lower troposphere is going up.
Friis-Christensen and Lassen suggested that the solar cycle length rather than sunspot numbers should represent solar activity because its variation closely matches the long-term variations of the Northern Hemisphere land air temperature during the past 130 years. Sallie Baliunas and Willie Soon showed that the 22-year or the 11-year magnetic cycle length correlates with the reconstructed temperature between 1750 and 1980. The shorter the solar cycle becomes, the stronger the solar activity and the higher the surface temperature becomes.
The solar cycle length, however, has not correlated with temperature since 1990. The recent raw data of the 11-year minimum-to-minimum solar cycle length are 119 months (July 1876-June 1986), 124 months (June 1986-October 1996), and 125 months (October 1996-April 2007). The solar cycle gets longer. At least it does not get shorter. Yet, the temperature has been rising since 1990. Nothing but the greenhouse effect can account for the recent warming.
2.2. The Methane Mystery
Methane is the third most influential greenhouse gas next to water vapor and carbon dioxide. Methane concentration has risen to an abnormal height.
The measured concentrations of the three greenhouse gases fluctuated only slightly (within 4% for CO2 and N2O and within 7% for CH4) over the past millennium prior to the industrial era, and also varied within a restricted range over the late Quaternary. Within the last 200 years, the late Quaternary natural range has been exceeded by at least 25% for CO2, 120% for CH4 and 9% for N2O.
Over the last 650 thousand years, methane concentration varied from lows of about 400 ppb during glacial periods to highs of about 700 ppb (parts per billion) during interglacial periods, but it reached 1774.62 ± 1.22 ppb in 2005.
We all know that burning fossil fuels has raised carbon dioxide concentration enormously. How can we explain the even more enormous rise in methane concentration? Because the source of atmospheric methane is not so well known as that of carbon dioxide, it is called “methane mystery". Anyway, it is unlikely that natural processes (wetlands, termites, oceans, vegetation, etc.) have brought unusual change. So, we must investigate what anthropogenic process contributes to the methane concentration change the most.
According to D. I. Stern and R. K. Kaufmann, the biggest man-made factor is livestock farming and the next biggest is rice crop farming. Ruminant animals such as cattle, goats, and sheep emit methane from enteric fermentation, when they belch or fart. The water of a rice paddy offers anoxic environments to biological fermentation. Both livestock farming and rice crop farming are functions of the population. The larger the human population becomes, the bigger the demand for meat, dairy products, and rice gets. Farming usually generates wastes that emit methane. Landfills account for another anthropogenic emission of methane.
Most of the methane in Earth’s atmosphere is thought to originate from biological fermentation, although it is also emitted through a non-fermentation process such as biomass burning, coal mining, and leakage from oil/gas supply systems. But these non-fermentation emissions do not amount to such large quantities as those of farming and landfills.
Methane does not remain in the atmosphere permanently. It is removed by the reaction with hydroxyl free radicals, which the photolysis of ozone and the subsequent reaction with water molecules bring about. Anthropogenic carbon monoxide from automobile and industrial emissions reacts with hydroxyl radicals that would otherwise remove methane, thus resulting in the rise in methane concentration. But most of the carbon monoxide in the atmosphere originates from natural sources, especially volcanic activities and bushfires.
The growth rate of methane concentration has, however, decreased since 1991, and the concentration has remained relatively constant since 1999, as the two graphs below indicate. This recent trend adds another methane mystery.
The graph of its growth rate:
Observatoire de Paris analyzed the factors of concentration fluctuation and concluded as follows.
The stalled atmospheric CH4 growth rate observed after 1992 is explained by a decline of anthropogenic emissions throughout the 1990s. In the most recent years, anthropogenic emissions have risen up, especially in North Asia, but their impact was hidden by a coincident decrease in wetland emissions.
In 1991, Mount Pinatubo in the Philippines erupted and emitted voluminous carbon monoxide, which decreased hydroxyl free radicals in the air and prolonged the life of atmospheric methane. That is why the growth rate jumped temporally in 1991.
Why did the growth rate get stalled thereafter? It is true that the growth rate of the human population has decreased recently. Economic incentives have led to a reduction in methane emissions from oil/gas supply systems, biomass burning, and coal mining. But these factors seem to be insufficient and cannot help to account for the fact that “anthropogenic emissions have risen up, especially in North Asia" in the most recent years.
What happened before 1992? In 1991, the Soviet Union was dissolved and the cut of timber decreased. Until then the Soviet Union had cut a huge amount of timber of Siberian taiga. Half of the cut wood was left to rot and emit methane. Moreover, their clear-cut logging exposed permafrost to the sunlight and let it thaw. The permafrost is rich in methane hydrate, a solid form of water that contains plenty of methane within its crystal structure. Therefore, the logging must have released much methane. Though the demand for timber remains low in Russia, Russians are cutting more and more timber to export it to Asia, especially to Japan. It may be the reason “anthropogenic emissions have risen up, especially in North Asia".
Another possible factor is the variation of natural gas production in North Asia. It peaked in 1990 and dropped thereafter. The recent rise in energy cost spurred Russians to enlarge natural gas production. The leakage from oil/gas supply systems has diminished globally, but in Russia, the gas supply system is still defective. So, the increase in natural gas production in Russia entails an increase in methane emissions.
Methane is useful if we utilize it, but harmful, if we release it into the air. Russia should utilize wood and methane as resources more effectively. The methane hydrate in the permafrost is difficult to collect and utilize, but it is nonetheless a resource that we should utilize. More methane hydrate deposits have been found under sediments on the ocean floors. If the temperature continues rising, the trapped methane will be released and increase the temperature further.
This positive feedback is called a runaway greenhouse effect, which is thought to have brought about the Permian-Triassic extinction event. To prevent such a disaster, we should extract methane from the deposits and use it as fuel, before it is released into the air as the high-powered greenhouse gas.
2.3. Deforestation and Desertification
Plants along with the oceans are major natural carbon dioxide sinks. The population explosion has brought about deforestation and desertification, which could account for the rise in carbon dioxide concentration. The 4th Assessment Report estimates land-use changes have likely contributed about a quarter of the current radiative forces, while the remainder was caused by emissions of fossil fuels and cement production.
The Kyoto Protocol, therefore, enacts that “additional human-induced activities related to changes in greenhouse gas emissions by sources and removals by sinks in the agricultural soils and the land-use change and forestry categories shall be added to, or subtracted from, the assigned amounts for Parties“. The 6th Conference of the Parties (COP6) of the United Nations Framework Convention on Climate Change (UNFCCC) agreed to regard forest and cropland management as activities that absorb carbon dioxide from the atmosphere and store it.
Some criticize this modification, pointing out that just keeping forests does not reduce carbon dioxide concentration, because they emit carbon dioxide when they are decomposed at the end. It is true that bushfires release much carbon dioxide, but not all carbon incorporated in plants is released into the atmosphere as carbon dioxide. The dead trees, plants, and moss are decomposed in peat bogs, which fix more carbon from the atmosphere than is released into it.
After generations and millennia, much of the carbon stored in plants moves to the soil, such that currently the global soil carbon sink is about three times larger than that of global standing live vegetation.
This carbon sequestration in vegetation has stored today’s fossil fuels such as coal, petroleum, and natural gas. They are renewable energy sources in this sense, though we consume them by far faster than they are produced. We have to shorten the process to extract energy from biomass. Plants’ incorporation of carbon dioxide slows down when they become mature. Using mature plants as biomass fuels and reforesting at the same time can reduce the consumption of fossil fuels and thus the emission of carbon dioxide.
So, not only afforestation or reforestation of deserts but also the forest and cropland management can contribute to the solution of global warming problems. Some scientists, however, suspect that plants emit another greenhouse gas, methane.
In 2006, Frank Keppler at the Max Planck Institute in Germany announced his team had detected methane exhaled from living terrestrial plants in an oxygen-rich environment. It was surprising news because most of the methane from natural sources in Earth’s atmosphere is thought to originate from fermentation. Though the lifetime of methane is shorter than carbon dioxide, its greenhouse effect is twenty-one times as large as that of carbon dioxide. If Keppler’s discovery should be true, plants might increase rather than decrease the greenhouse effect.
In 2007, however, Tom Dueck at Wageningen University in the Netherlands reported his team’s independent investigations showed that plants’ methane emissions are zero or very small at best. They grew six plant species in 13C-carbon dioxide atmosphere and measured 13C-methane emission and found that there is no evidence for substantial aerobic methane emission by terrestrial plants, maximally 0.3% of the values that Keppler reported.
So if Dueck’s team is correct, where did Keppler go wrong? Dueck suggests that Keppler’s team might have forgotten that gas trapped in plants’ intercellular spaces, and in air pockets in the soil, could diffuse out and be counted as ’emitted’ by the plant in their experiment.
But Keppler denies this, saying that this sort of methane desorption could only be partially responsible for the amounts of gas he found. Indeed, he suggests that Dueck’s use of heavy isotopes may have actually changed the plants’ metabolic preferences, killing off their methane emissions. Dueck counters that no literature reports suggest this might be a problem.
Now it becomes quite doubtful whether plants emit methane or not. Keppler thought pectin, the structural plant component, might play a prominent role in the formation of CH4, but the mechanism is unknown. The laws of thermodynamics don’t favor methane production under aerobic conditions. The debate is still going on, but we can dismiss this possibility for the present.
Another greenhouse gas that plants certainly emit is water vapor. A fully-grown tree evaporates a few cubic meters of water on a hot dry day. But the transpiration is not a serious problem, because saturated vapor returns to the ground as rain. Water vapor, though the strongest greenhouse gas, cannot be the primary cause of global warming. Moreover, transpiration absorbs the heat of evaporation, causing the surroundings to cool.
There is another way plants account for global warming. Regression of plant cover has been known to lower the surface temperature owing to high albedo of deserts. The IPCC 4th Assessment Report estimates the radiative forcing of the albedo change to be –0.2W/m2. It is not as high as that of the albedo change owing to aerosol emission (–0.5W/m2), but not negligible. Yet the assertion that desertification is desirable because of this negative radiative forcing is no less absurd than the assertion that air pollution is desirable because of its negative radiative forcing. Reflecting solar radiation without using it as fuel for life is a waste of low entropy energy and the resultant cooling is, therefore, not desirable.
Plants’ photosynthesis absorbs carbon dioxide and their transpiration absorbs the heat of evaporation, thus contributing to mitigate global warming. A decrease in albedo and an increase in water vapor accounts for a rise in temperature, but both are necessary for living systems. Plants play an important role in circulating water and nutrients. We should keep on trying to stop desertification.
3. The Impacts of Global Warming
Global warming has not only bad impacts but also good impacts on humans. Good impacts are scarcely told, but I must mention it briefly.
Temperature does not rise equally on the Earth. The higher latitude a place is located at, the bigger the rise in temperature is. This means cold regions become warmer, while hot regions do not become so hotter. The warming in cold regions will reduce energy demand for heating and human mortality from cold exposure. The warming promotes evaporation, increases precipitation, and makes access to freshwater easier. High temperature, ample water, and carbon dioxide encourage photosynthesis and result in high crop yields.
There are more negative impacts that offset these positive impacts of global warming, as I will explain in this section. The IPCC 4th Assessment Report regards more than 2-3°C temperature rise as critical.
For increases in global mean temperature of less than 1-3°C above 1990 levels, some impacts are projected to produce benefits in some places and some sectors, and produce costs in other places and other sectors. It is, however, projected that some low latitude and polar regions will experience net costs even for small increases in temperature. It is very likely that all regions will experience either declines in net benefits or increases in net costs for increases in temperature greater than about 2-3°C
There are two sorts of problems that global warming would incur, problems of temperature rising and those of temperature changing. First I will examine the latter.
3.1. Problems of Temperature Change
The temperature changing is a risk, whether it is cooling or warming. Sea level fluctuation is, for example, such a risk. Warming raises the sea level and cooling lowers it. Both fluctuations are inconvenient for harbor facilities usage. If sea level drops, berthing will be difficult and ships will be prone to grounding. Of course, it is just a temporary problem and we only have to build another harbor at an appropriate place. Sea level rise, on the other hand, causes more intractable and universal problems. Even a small-scale rise will increase the risk of flood and a large-scale rise will narrow our inhabitable area.
The IPCC 4th Assessment Report estimates the total 20th-century rise to be 0.17 (from 0.12 to 0.22) m and projects sea level to rise between the present (1980–1999) and the end of this century (2090–2099) under six scenarios by 0.18 to 0.59 m.
In the 1980s, America’s Environmental Protection Agency expected sea level to rise by several meters by 2100, but now the rising speed turns out to be lower than expected. Global warming has melted ice in the Polar Regions, but it is the ice floating in the sea that melts first, which does not result in sea level rise. Observed sea level rise between 1993 and 2003 was 3.1 ± 0.7 mm per year, of which more than half (1.6 ± 0.5 mm per year) was due to thermal expansion of seawater.
How high will the sea level be after the 21st century?
There is medium confidence that at least partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic ice sheet, would occur over a period of time ranging from centuries to millennia for a global average temperature increase of 1- 4°C (relative to 1990-2000), causing a contribution to sea level rise of 4-6 m or more.
Since the large-scale rise will take more than 100 years and the life of facilities will be over before they sank underwater, shifting inhabitants gradually to the higher location would be more feasible measures and cost less than building breakwaters. The trouble is we cannot predict the exact rise.
Another problem of temperature change is the increase in extinct species. Ecosystem multifunctionality requires greater numbers of species. In order to maintain biodiversity, a stable temperature is the most desirable. Both warming and cooling entail the change of environment and are threats to species that adapt themselves to their special environment.
Approximately 20-30% of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5-2.5°C.
Chris Thomas et al (2004) drew similar conclusions from their simulation.
Using projections of species’ distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth’s terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be ‘committed to extinction’.
Coral species, for example, live within a narrow temperature zone, and both low and high sea temperatures can induce coral bleaching. Besides the impact from temperature rising, anthropogenic emissions of carbon dioxide have already led to a reduction in the average pH of surface seawater of 0.1 units and could fall by 0.5 units by the year 2100. The impact of acidification will be severe for coral reefs.
Coral species make calcium carbonate from carbonate ions and calcium ions, which carbon dioxide and rock dissolved in water respectively produce. After death, coral reefs store the calcium carbonate as limestone. If coral reefs drastically diminish or become extinct, the ocean will absorb less carbon dioxide, thus promoting further warming.
You might think, “The climate change might reduce biodiversity temporarily, but adaptive radiation of surviving species can fill ecological niches the distinction will open. The history of life is a succession of extinction. We don’t have to worry about the extinction of species unless humans are included in them." I will examine later whether global warming is harmful to life in general or not. Anyway, the extinction or decrease of species useful for humans is inconvenient, even if it is temporary.
3.2. Problems of Temperature Rising
Global warming is projected to have impacts on precipitation. The hotter it becomes, the more water evaporates. According to the Clausius-Clapeyron relation, the water-holding capacity of the atmosphere increases by about 7% for every 1°C rise in temperature. The 4th Assessment Report estimates that over the 20th-century atmospheric water vapor increased by about 5% in the atmosphere over the oceans. The rise in temperature should increase precipitation, but the fact is not so simple.
As the figure below shows, rainfall has been decreasing and has recently started to increase again, while temperatures have been increasing since 1976. Even if the saturated water vapor increases, global warming will not bring about an increase in rainfall if the water cycle remains stagnant.
Precipitation over the oceans in the latitude range between 25°S and 25°N increased about 4% over the 25 years, with a partially compensating 2% decrease over land in the same latitude belt. Global warming should increase the rainfall of the Intertropical Convergence Zone (ITCZ) where the Hadley Cell ascends. The decrease in rainfall over land would be due to anthropogenic desertification. Northern mid-latitudes where the Hadley Cell descends show a decrease over land and ocean. Global warming encourages evaporation at the horse latitudes without supplying them with moisture. High latitudes can enjoy more rainfall.
The dry regions become drier and wet regions become wetter. The 4th Assessment Report expects this tendency to continue in the future.
By mid-century, annual average river runoff and water availability are projected to increase by 10-40% at high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes and in the dry tropics, some of which are presently water stressed areas.
What influence will global warming have on plants? Because carbon dioxide is the material of photosynthesis, the rise in its concentration itself has a good influence on plants. This effect is called CO2 fertilization. Crops show an average increase in net primary production of around 33% for a doubling of atmospheric CO2. Especially at high latitudes, an increase in rainfall and a rise in temperature are expected to bring about a good harvest.
To be sure, the rise in carbon dioxide concentration causes a good yield of plants, though the marginal yields diminish. This is because there are other factors that determine the speed of photosynthesis, say, water supply, nutrients, solar radiance, genetic limitations on growth, etc. Plants have their unique optimum temperature for their ripening and the temperature above or below it harms them. So, breed improvement or adoption of another crop species would be necessary to cope with climate change.
Generally speaking, moderate global warming will have a positive influence on the farming in advanced countries located at high latitudes, where it rains much, severe coldness is mitigated, farmers have enough money and technology for fertilization, irrigation, and breed improvement, but global warming, even if it is a slight rise in temperature, will have a negative influence on the farming in developing countries located at low/mid-latitudes.
Another concern is abnormal weather. The 4th Assessment Report regards it as likely (66 to 90% probable) that global warming will increase intense tropical cyclone activity. The expected rise in sea level is very small (0.18-0.59m), but even a slight rise in sea level will increase the risk of food if the increase in cyclones accompanies it.
The dispute over the causal relationship between global warming and an increase in intense tropical cyclone activity is yet to achieve consensus among scientists. In 2005, Christopher Landsea withdrew from his participation in the IPCC 4th Assessment Report, accusing Kevin Trenberth of misrepresenting the effect of Global Warming on hurricane activity.
He considers the hurricane activities cyclic, pointing out that 1948-1964 had as many hurricanes as 1995 and beyond, and questions the common belief that global warming is the cause of the high number of hurricanes since 1995.
Researchers including Landsea say:
One may ask whether the increase in activity since 1995 is due to anthropogenic global warming. The historical multidecadal-scale variability in Atlantic hurricane activity is much greater than what would be “expected" from a gradual temperature increase attributed to global warming […] The possibility exists that the unprecedented activity since 1995 is the result of a combination of the multidecadal-scale changes in Atlantic SSTs (and vertical shear) along with the additional increase in SSTs resulting from the long-term warming trend. It is, however, equally possible that the current active period (1995-2000) only appears more active than the previous active period (1926-1970) due to the better observational network now in place.
If Atlantic hurricane activity cycles, as he assumes, it will calm down in the near future, although global warming continues. The controversy between Christopher Landsea and Kevin Trenberth will also calm down when the result is shown.
The most paradoxical problem of temperature rising is the shutdown or slowdown of the ocean conveyor and resulting cold weather in the North Atlantic. The ocean conveyor belt that sinks in the North Atlantic Ocean, floats to the Pacific Ocean, and gradually returns to the Polar Regions is called thermohaline circulation (THC), because it conveys heat and sunken nutrition. It is also called meridional overturning circulation (MOC).
When it gets rapidly hot, ice in the Polar Regions melts, which in turn decreases surface layer salinity and, because fresh water is less dense than saline water, this freshening slows the sinking and the deepwater formation process. So, the shutdown or slowdown of THC is assumed to trigger localized cooling in the North Atlantic and lead to cooling in that region. The movie, The Day After Tomorrow, has made this hypothesis famous.
Some scientists doubt the hypothesis. Peili Wu et al. showed that an ensemble of Had CM3 simulations reproduces the observed freshening trend, but this freshening coincides with a strengthening rather than a weakening trend in the THC.
From the model simulations, we can trace such a freshening trend to the Arctic Ocean where sea surface salinity undergoes a large decreasing trend due to melt ice and river runoff during the same period. However, we do not find a decreasing trend of the North Atlantic THC. On the contrary, the THC has an upward trend diagnostically associated with an increased north-south upper ocean density gradient between the sub-polar North Atlantic and the mid-low latitudes.
If the decrease in sea surface salinity does not weaken THC, the hypothesis requires further examination.
3.3. The Essence of the Problem
In order to understand the essence of the global warming problem, we must distinguish good warming from bad warming.
Living systems maintain themselves by making the low-entropy energy from the high-temperature source (mainly solar radiation) and discharge the high-entropy waste into the low-temperature sink (mainly water and ultimately outer space). The increase in solar flux raises the surface temperature of the earth and this is good warming, because more solar radiation brings more low-entropy resources to living systems and promotes water circulation, thus improving water availability to them.
On the other hand, warming due to greenhouse effects is bad warming. Greenhouse gasses absorb heat radiation from the surface earth and send back part of it to the ground so that the increase in greenhouse gasses accumulates high-entropy waste heat in the atmosphere. The problem of global warming is the problem of waste disposal. Though the rise in temperature itself can be an accidental advantage for some species over others, the increase in entropy is a universal disadvantage for all species, because it brings the atmosphere close to heat death.
Based on the distinction between good warming and bad warming, we can draw a distinction between good cooling and bad cooling. Volcanic eruption and anthropogenic air pollution prevent solar radiation from reaching the surface earth and drop the temperature. This is bad cooling because it reduces incoming resources. On the other hand, the reduction of greenhouse gasses makes it easy to throw waste heat into outer space and drop the temperature. This is good cooling because it reduces the entropy of the atmosphere.
The distinction is very important. Some scientists, who alarm the threat of global warming without distinguishing good warming from bad warming, consider the temperature rise to be harmful and propose prescriptions that try to set off bad cooling against bad warming.
Dr. Roger Angel, an astronomer at the University of Arizona, who suggests a space sunshade plan, is one of them. His plan is to launch a constellation of many small free-flying spacecraft a million miles above the Earth into the inner Lagrange point (L1) and to block 1.8% of the solar flux with the space sunshade. The spacecraft are transparent to minimize radiation pressure but still can reduce the light from the Sun. He presented the idea at the National Academy of Sciences and won a NASA Institute for Advanced Concepts grant for further research in 2006.
Dr. P.J. Crutzen, a Dutch Nobel prize winning atmospheric chemist, proposed a method of artificially cooling the global climate “by burning S2 or H2S, carried into the stratosphere on balloons and by artillery guns to produce SO2“. The chemical and microphysical processes in the stratosphere convert SO2 into sub-micrometer sulfate particles and they would certainly artificially enhance the earth’s albedo and cool climate.
Reducing solar flux to mitigate global warming is like reducing meals to mitigate constipation. It is true that reducing meals will reduce excrement, but it does not cure constipation. Humans take in food, increase its entropy and discharge it. If intake of low-entropy resources and discharge of high-entropy waste stagnate, it will hit living systems doubly hard.
Global warming is, so to speak, the constipation of the earth’s system. What is necessary to relieve the earth’s constipation is to reduce not solar influx but hindrance to discharge waste heat. This solution is similar to that for usual constipation.
The accumulation of waste heat is not so serious globally as locally in the city. The city not only emits much heat but also easily traps it because buildings cut off wind and there are few plants whose transpiration absorbs heat. The urban heat island effect is different from the greenhouse effect, but the heat damage to living systems is of similar nature.
The 4th Assessment Report thinks little of an urban heat island effect because cities occupy only 0.046% of the entire surface of the earth and the radiative forcing of urban heat islands is only 0.03W/m2. But we should be concerned about the influence of global warming on urban heat islands rather than that of urban heat islands on global warming.
Another popular heat problem is the heat wave. The cause of the recent rise in heat waves is partly natural and partly anthropogenic, that is to say, the modern population explosion and its results (urbanization, desertification, and global warming) must have something to do with it.
The heat waves in the United States and Europe have the character of large-scale urban heat islands because they are the most advanced areas of western civilization or, so to speak, the cities of the world. The heat waves in Australia are coincident with its desertification. Global warming also accounts for heat waves. When Europe had one of the hottest summers on record in 2003, Hadley Centre said,
When man-made climate change is omitted, extreme warm events are likely to occur very rarely; most likely, once every 1,000 years. However, when man-made changes are included, the same event is likely to occur much more frequently; most likely, once every 250 years. […] It is very likely that at least half the risk of the European 2003 heatwave was due to human activity, mainly fossil fuel burning.
Greenhouse gasses increase not only thermal entropy but also information entropy. What effect global warming will have is uncertain. Something we never anticipate might happen in the future. The more uncertain our future becomes, the more our information entropy becomes.
We can easily adapt to stable instability, such as the change of the seasons. What is harmful to life is unstable instability. For example, many French died of 37-38 centigrade hot days, but those who are accustomed to such high temperatures every summer do not die of the same temperature. If we know the exact information of sea-level rise in advance, we can adapt the urban design to it. If we know the exact information of precipitation and temperature in advance, we can adapt agriculture to it. Uncertainty about the undesirable itself is more undesirable.
Both temperature level and temperature rising rate are not abnormal at present. The abnormality of today’s global warming consists in its cause. It is caused by the increase in not solar flux but the greenhouse effect so that the entropy of the atmosphere is increasing. The problem of global warming is also the problem of entropy.
- Intergovernmental Panel on Climate Change. Climate Change 2007 – The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the IPCC.
- Intergovernmental Panel on Climate Change. Climate Change 2007 – Impacts, Adaptation and Vulnerability. Working Group II Contribution to the Fourth Assessment Report of the IPCC.
- Intergovernmental Panel on Climate Change. Climate Change 2007 – Mitigation of Climate Change. Working Group III Contribution to the Fourth Assessment Report of the IPCC.
- United Nations Environment Programme. Global Deserts Outlook. United Nations (June 16, 2006).
- ↑Newsweek (1975) The Cooling World, April 28, 1975. p.64.
- ↑Data from Global Historical Climate Network (2007) GLOBAL Temperature Anomalies in .01 C.
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.98. The cited papers in this quotation are Reid A. Bryson and Gerald J. Dittberner (1976) A Non-Equilibrium Model of Hemispheric Mean Surface Temperature, Journal of the Atmospheric Sciences, 33. p.2094-2106; Stanley F. Woronko (1977) Comments on “A Non-Equilibrium Model of Hemispheric Mean Surface Temperature", Journal of the Atmospheric Sciences, 34. p.1820-1821; Reid A. Bryson and Gerald J. Dittberner (1977) Reply, Journal of the Atmospheric Sciences, 34. p.1821-1824.
- ↑Science Mission Directorate. “Accurate “Thermometers" in Space." October 2, 1997. Data from John Horack, Roy Spencer (1997) NASA satellite temperature measurements fuel Global Warming debate, NASA.
- ↑Data from John R. Christy (2007) Channel 2 Retrieval of the Lower Troposphere, Earth System Science Center University of Alabama in Huntsville.
- ↑United States Senate (1997) Global Climate Change, Hearings before the committee on environment and public works, One hundred fifth congress, First session on reviewing the effects of greenhouse gases on global weather conditions and assessing international policy options to reduce the negative impacts of climate change, July 10 and 17.
- ↑Data from John R. Christy (2007) Channel 2 Retrieval of the Lower Troposphere, Earth System Science Center University of Alabama in Huntsville.
- ↑MetOffice."Tropospheric and stratospheric temperatures" in “Hadley Centre: Climate monitoring“.
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.267.
- ↑However, the Vienna Convention and the Montreal Protocol have regulated the emission of ozone-depleting substances, and as a result, the ozone layer has been restored and the stratospheric temperature has recently begun to rise. For more information, refer to: Philipona, Rolf, Carl Mears, Masatomo Fujiwara, Pierre Jeannet, Peter Thorne, Greg Bodeker, Leopold Haimberger, et al. “Radiosondes Show That After Decades of Cooling, the Lower Stratosphere Is Now Warming.” Journal of Geophysical Research: Atmospheres 123, no. 22 (2018): 12,509-12,522.
- ↑Parker, David E. “Large-Scale Warming Is Not Urban.” Nature 432, no. 7015 (November 2004): 290–290.
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.9
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.5
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.465.
- ↑Richard B. Alley (2000) Ice-core evidence of abrupt climate changes, Proceedings of the National Academy of Sciences, Vol. 97, Issue 4. p. 1331-1334
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.192
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.131
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.114.
- ↑Data from C.D. Keeling T.P. Whorf, and the Carbon Dioxide Research Group Scripps Institution of Oceanography (2005) [http://cdiac.ornl.gov/ftp/trends/co2/maunaloa.co2 Atmospheric CO2 concentrations (ppmv) derived from in situ air samples collected at Mauna Loa Observatory, HawaiiUniversity of California La Jolla, California USA.
- ↑Data from Global Historical Climate Network (2007) GLOBAL Temperature Anomalies in .01 C.
- ↑Data from US National Geophysical Data Center (2007) Sunspot Number.
- ↑Data from John R. Christy (2007) Channel 2 Retrieval of the Lower Troposphere, Earth System Science Center University of Alabama in Huntsville.
- ↑Friis-Christensen, E., and K. Lassen (1991) Length of the solar cycle: An indicator of solar activity closely associated with climate, Science, Vol. 254. No. 5032, pp. 698 – 700.
- ↑Sallie Baliunas, Willie Soon (1995) Are Variations in the Length of the Activity Cycle Related to Changes in Brightness in Solar-Type Stars? Astrophysical Journal, Vol.450. p.896
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.447.
- ↑Stern, David, and Robert Kaufmann. “Annual Estimates of Global Anthropogenic Methane Emissions: 1860-1994.” Environmental System Science Data Infrastructure for a Virtual Ecosystem; Carbon Dioxide Information Analysis Center (CDIAC), Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States), 1998.
- ↑Data from CSIRO Atmospheric Research and Cape Grim Baseline Air Pollution Station, Australian Bureau of Meteorology (2006) Monthly averaged atmospheric methane (CH4) data.
- ↑“La réduction du taux de croissance atmosphérique de CH4 est expliquée par une réduction des émissions anthropogéniques dans les années 1990. Depuis 1999, les émissions anthropiques augmentent de nouveau, surtout en Asie du Nord. Cependant, le taux de croissance de CH4 reste faible à cause d’une réduction simultanée des émissions liées aux zones inondées, probablement à cause de sécheresses récurrentes." ― Observatoire de Paris. “Les causes naturelles et anthropiques de la variabilité du méthane atmosphérique – Observatoire de Paris – PSL Centre de recherche en astronomie et astrophysique.” 1er septembre 2006.
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.131.
- ↑The United Nations (1998) The Kyoto Protocol to the United Nations Framework Convention on Climate Change, Article 3.4.
- ↑The details of this modification were decided at COP7 held at Marrakesh from 29 October to 10 November 2001. See The United Nations Framework Convention on Climate Change (2001) Report of the conference of the parties on its seventh session, Decision 11.
- ↑United Nations Environment Programme. Global Deserts Outlook. United Nations (June 16, 2006). p.53.
- ↑Frank Keppler, John T. G. Hamilton, Marc Bra and Thomas Röckmann (2006) Methane emissions from terrestrial plants under aerobic conditions, Nature 439, 187-191
- ↑Tom A. Dueck, Ries de Visser, Hendrik Poorter, Stefan Persijn, Antonie Gorissen, Willem de Visser, Ad Schapendonk, Jan Verhagen, Jan Snel, Frans J. M. Harren, Anthony K. Y. Ngai, Francel Verstappen, Harro Bouwmeester, Laurentius A. C. J. Voesenek, Adrie van der Werf (2007) No evidence for substantial aerobic methane emission by terrestrial plants: a 13C-labelling approach, New Phytologist, Volume 175, Issue 1. p. 29-35.
- ↑Chemistry World (2007) Scientists clash over methane mystery, 27 April.
- ↑Charney, J.G. (1975) Dynamics of deserts and drought in the Sahel, Quarterly Journal of the Royal Meteorological Society 101: 193–202
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.4.
- ↑Intergovernmental Panel on Climate Change (2007) Impacts, Adaptation and Vulnerability, Climate Change 2007: Fourth Assessment Report. p.17.
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.4
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.750.
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.7
- ↑Intergovernmental Panel on Climate Change (2007) Impacts, Adaptation and Vulnerability, Climate Change 2007: Fourth Assessment Report. p.17
- ↑Andy Hector, Robert Bagchi (2007) Biodiversity and ecosystem multifunctionality, Nature 448, pp.188-190
- ↑Intergovernmental Panel on Climate Change (2007) Impacts, Adaptation and Vulnerability, Climate Change 2007: Fourth Assessment Report. p.7
- ↑Chris D. Thomas et al. (2004) Extinction risk from climate change, Nature, Vol. 427. p. 145.
- ↑The Royal Society (2005) Ocean acidification due to increasing atmospheric carbon dioxide, The Clyvedon Press Ltd. p.6.
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.262
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.260
- ↑Intergovernmental Panel on Climate Change (2007) Impacts, Adaptation and Vulnerability, Climate Change 2007: Fourth Assessment Report. p.6.
- ↑G.W. Koch, H.A. Mooney (1996) Response of terrestrial ecosystems to elevated CO2: a synthesis and summary, Carbon Dioxide and Terrestrial Ecosystems, Academic Press, San Diego, pp. 415-429.
- ↑Intergovernmental Panel on Climate Change (2007) Impacts, Adaptation and Vulnerability, Climate Change 2007: Fourth Assessment Report. p.15.
- ↑S.B. Goldenberg, C.W. Landsea, A.M. Mestas-Nuñez, W.M. Gray (2001) The Recent Increase in Atlantic Hurricane Activity: Causes and Implications, Science, Vol. 293. No. 5529. p. 474 – 479.
- ↑P. Wu, R. Wood, P. Stott (2004) Does the recent freshening trend in the North Atlantic indicate a weakening thermohaline circulation?, Geophysical Research Letters, vol.31, l02301.
- ↑Roger Angel (2006) Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1), Proceedings of the National Academy of Sciences, Vol. 103, No. 46, 17184-17189.
- ↑National Aeronautics and Space Administration (2006) Space Sunshade Might Be Feasible in Global Warming Emergency, Earth Observatory News.
- ↑UNIVERSITY OF ARIZONA. “Space Sunshade Concept."
- ↑Paul J. Crutzen (2006) Albedo Enhancement by Stratospheric Sulfur Injections: A Contribution to Resolve a Policy Dilemma? , Climate Change, Volume 77, Issue 3. p.211-219.
- ↑Intergovernmental Panel on Climate Change. The Physical Science Basis, Climate Change 2007: Fourth Assessment Report. Cambridge University Press; 1st edition (September 10, 2007). p.185
- ↑Hadley Centre (2004) Uncertainty, risk and dangerous climate change Recent research on climate change, METOffice. p.9.