Climate change

While the term global warming in general refers to any rise in the average temperature of the earth's atmosphere, in public policy discussions, global warming usually means excessive and harmful warming leading to a worldwide catastrophe. When global warming is attributed to man-made causes, it is called anthropogenic global warming.

Climate scientists agree that the earth's temperature has fluctuated throughout history by about 3 degrees Celsius (5 degrees Fahrenheit). For example, about 300 years ago, the Earth was experiencing the Little Ice Age It had descended into this relatively cool period from a warm interval about 1,000 years ago known as the Medieval Climate Optimum

Global Warming Catastrophe

At issue now is whether the latest global warming period will continue indefinitely as many fear. Scientists are divided on whether this catastrophe is likely to occur.

The earth has seen a significant increase in average global surface temperature over the last 150 years. Many public policy organizations and government officials assert that this warming will continue indefinitely, rather than being followed by a period of global cooling as in the past. A temperature increase of 4 degrees Celsius would cause catastrophic harm to the environment.

Catastrophe proponents maintain that increased concentrations of anthropogenic greenhouse gases in the atmosphere correlate with global warming. Opponents point out that most of the 20th century's warming occurred before 1940, followed by a brief period of cooling. The IPCC, a United Nations science and public policy organization, published a report saying that scientists believe that anthropogenic greenhouse gases "play an important role in global warming."

Evidence for and against the catastrophe hypotheses

The main evidence for global warming comes from thermometer measurements from land stations all over the world since 1860. The data show that the average surface temperature has increased by 0.6±0.2 C during the 20th century. Most of the warming occurred during two periods: 1910 to 1945 and 1976 to 2000. (Source: IPCC).

The trend line for NOAA data from 1979 to 1998 shows a tiny amount of global cooling (0.01 degrees centigrade per decade), which contradicts the IPCC prediction of 0.4 degrees of warming per decade. (Source: NASA Science News 14 August 1998) Moreover, the R-squared coefficient of the trend line is too small to indicate a significant trend. The data from these measurements are not even mentioned in their report, leading opponents to charge the IPCC with political bias.

To do: include IPCC response to NOAA data.

The Intergovernmental Panel on Climate Change's (IPCC) 1995 estimate of average global warming at the surface until the year 2100 is +0.18 °C/decade. Climate models suggest that the deep layer measured by the satellite and weather balloons should be warming about 30% faster than the surface (+0.23 °C/decade). None of the satellite or weather balloon estimates are near this value. (Source: NASA Science News 14 August 1998)

The IPCC says that it has corrected the land station data to account for the urban heat island effect. To do: find and summarize their corroction technique.

Secondary evidence comes from observed variations on the snow cover and ice extent, global average sea level, precipitation, cloud cover, El Nino and extreme weather events during the 20th century. For example, satellite data shows a 10% decrease of snow cover since the late 1960s. The Northern Hemisphere spring and summer sea-ice extent has decreased by about 10% to 15% since the 1950s and there has been a widespread retreat of mountain glaciers in non-polar regions throughout the 20th century. (Source: IPCC). In January 2002, scientists released data showing that the Antarctic ice cap had grown about 25%, which contradicts the IPCC's prediction that the ice cap would shrink.

Climate change factors

Climate changes occur due to internal and external factors. Internal factors are factors associated with the complexity of the climate systems which are chaotic non-linear systems. External factors can be natural factors and anthropogenic factors.

Natural Causes

The main natural external factor is the variability in the amount of solar radiation that reaches Earth. The solar radiation can change because of solar cycles, because of cyclic changes in the Earth's orbit, and because the Sun is getting hotter. Anthropogenic factors are related to changes in the environment influenced by Man. The main anthropogenic factors are the emission of greenhouse gases, the depletion of stratospheric ozone, changes in land use and the emission of aerosols such as sulphates. (Source: IPCC)

Scientists agree that internal factors and natural external factors can cause significant climate changes. In the last millennium, two important periods occurred: a warm period known as the Medieval Warm Period and a cold period known as the Little Ice Age. These periods have a magnitude similar to the warming in the 20th century and it's agreed that they were cause by internal factors and natural external factors only. The Little Ice Age is usually attributed to the reduction of solar activity. Some scientists have claimed in the past that the observed warming since 1860 is a natural climate recovery from the Little Ice Age. (Source: The Skeptical Environmentalist)

Human Causes

However, large amounts of anthropogenic greenhouse gases were emitted to the atmosphere since the beginning of the industrial revolution. Since 1750, the carbon dioxide concentration has increased by 31%, methane has increased 151%, nitrous oxide has increased 17% and tropospheric ozone has increased 36%. (Source: IPCC)

The majority of these gases are produced by the combustion of fossil fuels. It is thought that the reduction in tropical forested area has also played a role, as old forests store large amounts of carbon. However, growing forests in North America and Russia contribute to absorb carbon dioxide (they act as CO₂ sinks) and since 1990, the amount of carbon absorbed is larger than the amount released by deforestation. Not all the CO₂ emitted to the atmosphere accumulates there. Half of it is absorbed by oceans and forests.

The real importance of each of the proposed causes can only be established through the exact quantification of every factor involved. Internal and external factors can be quantified by the analysis of climate simulations based on the best climate models.

The influence of external factors can be compared using the concept of radiative forcing. A positive radiative forcing warms the planet, and negative radiative forcing cools the planet. Anthropogenic emissions of greenhouse gases, stratospheric ozone depletion, and solar radiation have positive radiative forcing, whereas aerosols and land use changes have negative radiative forcing. (Source: IPCC)

Climate models

Climate simulations show that warming occurring from 1910 to 1945 can be explained by internal and natural forcing (variation in solar radiation) only, but proponents claim that warming occurring from 1976 to 2000 needs anthropogenic greenhouse gases emissions to be explained.

This conclusion depends on the accuracy of the models used and on the correct estimation of the external factors. The majority of scientists agrees that important climate features are incorrectly accounted by the climate models, but these scientists don't think that better models would change the conclusion. (Source: IPCC)

Critics point out that there are flaws in the models and external factors not taken into consideration that could change the conclusion above. The critics say that the climate simulations are unable to model the cooling effects of the particles, fitting the water vapor feedback and handling clouds. Critics also point out that the Sun may have a share of responsibility for the observed global warming greater than now thought by the majority of the scientific community. Some indirect solar effects may be very important and are not accounted by the models. So, the share of global warming caused by anthropogenic greenhouse gases may be lower than thought. (Source: The Skeptical Environmentalist)

Predicted Effects

Due to potential effects on human health, economy and the environment, global warming is the cause of great concern. Some important environmental changes have been observed and were linked to global warming. The examples of secondary evidence cited above (lessened snow cover, rising sea levels, weather changes) are examples of consequences of global warming that may influence not only human activities but also the ecosystems. Increasing global temperature means that ecosystems may change; some species may be forced out of their habitats (possibly to extinction) because of changing conditions while others may spread.

However, global warming can also have positive effects, since higher temperatures and higher CO₂ concentrations improve the ecosystems' productivity. Satellite data shows that the productivity of the Northern Hemisphere has increased since 1982. On the other hand, an increase in the total amount of biomass produced is not necessarily all good, since biodiversity can still decrease even though a small number of species are flourishing. Similarly, from the human economic viewpoint, an increase in total biomass but a decrease in crop harvests would be a net disadvantage.

Another cause of great concern is sea level rise. Sea levels are rising 0.01 to 0.02 meters per decade and some small countries in the Pacific Ocean are expressing concerns that if this rise in sea level doesn't stop, they soon will be entirely under water. Global warming causes the sea level to rise mainly because sea water expands, but some scientists are concerned that in the future, the polar ice caps and glaciers may melt. As a consequence, the sea level could rise several meters. At the moment, scientists are not expecting any major ice melting in the next 100 years. (Sources: IPCC for the data and The Mass Media for the general perception that climate change is important) Some researchers have found a negative correlation between sea level rise and average global temperature; water evaporates more quickly than it expands. (Source: SEPP)

As the climate gets hotter, evaporation will increase. This will cause heavier rainfall and more erosion. Many people think that it could result in more extreme weather as global warming progresses.

Global warming can also have other, less obvious effects. The North Atlantic drift, for instance, is driven by temperature changes. It seems as though it is diminishing as the climate grows warmer, and this means that areas like Scandinavia and Britain that are warmed by the drift might face a colder climate in spite of the general global warming.

The Intergovernmental Panel on Climate Change (IPCC)

Since it is such an important issue, governments need predictions of future trends in global change so they can take political decisions to avoid undesired impacts. Global warming is being studied by the Intergovernmental Panel on Climate Change (IPCC). In its last report, the IPCC made some predictions about future climate change. These predictions are the basis for current political and scientific discussion.

IPCC predictions are based on the same models used to establish the importance of the different factors in global warming. These models need data about anthropogenic emissions of greenhouse gases and aerosols. This data is predicted from economical models based on 35 different scenarios. Scenarios go from pessimistic to optimistic, and predictions of global warming depend on the kind of scenario considered. None of these scenarios consider any kind of measures to avoid global warming.

In its last report, IPCC stated that average surface temperature is projected to increase by 1.4 to 5.8 °C over the period 1990 to 2100, and the sea level is projected to rise by 0.1 to 0.9 meters over the same period.

IPCC prediction are supposedly the best predictions available but are under strong scientific scrutiny. The IPCC concedes that there is a need for better models and better scientific understanding of some climate phenomena, as well as the uncertainties involved. Critics point out that the available data is not sufficient to determine the real importance of greenhouse gases in climate change. Sensitivity of climate to greenhouse gases may be overestimated because of some flaws in the models and because the importance of some external factors may be underestimated.

On the other hand, predictions are based on scenarios and the IPCC did not assign any probability to the 35 scenarios used. Critics point out that some of the scenarios that predict the largest impacts are not realistic because they contradict basic economical reasoning.

The most important objection to the predictive models espoused by the IPCC is that they contradict the NOAA's weather balloon and satellite data. The IPCC's reports do not address this contradiction and in fact do not event mention the existence of the data.

The United Nations Framework Convention on Climate Change and the Kyoto Protocol

Even if there are some doubts about its importance, global warming is perceived by the general public and by some political leaders as a potential threat to human health and economic prosperity, especially in developing countries. Reductions of the emissions of greenhouse gases by developed countries was proposed, with developing countries such as India and China being exempted from any reductions. Being a tragedy of the commons-like problem, only an international agreement could reduce the emissions of greenhouse gases since voluntary reductions would be avoided by individual countries. Hence the global warming treaty will not take effect unless enough countries ratify it.

The United Nations Framework Convention on Climate Change (UNFCCC) establishes a process for developing an international response to the percieved global warming problem. Most of the countries in the world are parties to the UNFCCC, including all the major industrial nations. The UNFCCC, however, does not provide any binding emission targets.

Most of the parties to the UNFCCC, including all the major industrial nations, are party to the Kyoto Protocol to the UNFCCC, which proposes binding greenhouse gas limits for developed countries (developing countries are not subject to limits under the Protocol). The limits are based on the level of their emissions in 1990; most developed countries would be required to limit their emissions to a level below the 1990 level, although a few would be permitted to limit their emissions to a level higher than what they emitted in 1990 (e.g., Iceland).

The United States, responsible for one-third of the emissions of greenhouse gases, has signed the Kyoto Protocol, but the United States Senate and the Bush Administration have indicated that they do not intend to ratify it. This decision resulted in internal and international controversy with major political and ideological ramifications.

To evaluate the effectiveness of the Kyoto protocol, it is necessary to compare global warming with and without the agreement. Several independent authors agree that the impact of the Kyoto protocol on global warming is very small (a reduction of 0.15 in 2 C warming by 2100). Even some defenders of the Kyoto protocol agree that the impact of it is small, but they view it as a first step, with more political than practical importance, for future reductions. At the moment, an analysis made by the IPCC is needed to clarify this issue.

The Kyoto Protocol can also be evaluated by comparing costs and gains. Several economical analyses were made that show that the Kyoto Protocol is more expensive than the global warming that it avoids. Defenders of the Kyoto Protocol argue however that while the initial greenhouse gas cuts may have little effect, they set the political precedent for bigger (and more effective) cuts in the future.