The IPCC not only critically analyzes the scientific data regarding greenhouse gases and global climate change, but it makes model-based predictions on future changes according to various emission scenarios.10 If greenhouse gases were held at 2000 levels, the predicted temperature in 2090-2099 compared to 1980-1999 would increase by 0.6°C (likely11 range is 0.3-0.9°C) or 1.1°F. For the low emis­sion scenario, the increase is 1.8°C (1.1-2.9°C) or 3.2°F; for the high emission scenario (basically business as usual), the increase is 4.0°C (2.4-6.4°C) or 7.2°F (1). For the next two decades, there is expected to be warming of about 0.2°C per decade for the various emission scenarios, and there would be a warming of about

0. 1°C per decade even if all greenhouse gases and aerosols were kept constant at year 2000 levels (1). This is because of the slow warming response of the oceans and the very long time that CO2 remains in the atmosphere.

These temperature changes may not seem to be very large, but they have major consequences. In the third IPCC report in 2001, risks of climate change were assessed based on various “reasons for concern.” These reasons for concern include:

• Risks to unique and threatened systems, such as coral reefs, tropical glaciers, endangered species, unique ecosystems, biodiversity hotspots, small island states, and indigenous communities;

• Extreme weather events, such as heat waves, floods, droughts, and tropical cyclones;

• Distribution of impacts, with disparities between various regions and populations that may suffer greater harm, such as extensive drought or high sea levels, compared to those that may actually benefit;

• Aggregate impacts such as monetary damages and lives affected or lost;

• Risk of large-scale discontinuities such as partial or complete melting of Greenland or West Antarctica ice sheets.

A recent update on these reasons for concern based on more current publica­tions shows that all of these risks are greater at lower temperatures than were originally estimated in 2001 (47). This is dramatically illustrated in the famous “burning embers” graphic (Figure 1.10). A 2°C increase in temperature is now expected to have much more severe consequences than previously thought.