- Numerous other climate changes have also been observed including widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy precipitation, heat waves and intensity of tropical cyclones.
- These changes are having direct impact on humans. Changes to agricultural and forestry management in the northern hemisphere are being observed such as earlier spring planting of crops and forest disturbance caused by fires and pests. Some aspects of human health are being impacted such as heat-related mortality in Europe, increases in infectious disease and allergenic pollens in some areas. In the Arctic and northern regions hunting, travel over snow and ice, and mountain sports are affected.
Considering these observed changes, the IPCC finds that it is extremely unlikely (less than a five per cent probability) that global climate change over the past 50 years can be explained without external forcing, and very likely that the changing climate is not due to known natural causes alone. For example, an increase in solar output would be external. Volcanic eruptions are external. Human-caused changes in atmospheric composition are external.
Looking Forward
For the next two decades a warming of about 0.2°C per decade is projected globally. Projections for the rest of the century depend largely on the development path taken, meaning that the temperature rise by the year 2100 could be as low as 1.1°C with a shift to a highly renewable energy system or as high as 6.4°C with fossil-fuel use remaining much the same as today. In a warmer world, snow cover is projected to continue to contract, sea ice is projected to shrink and it is very likely that heat waves and heavy precipitation events will continue to be more frequent. Increases in the amount of precipitation are very likely at high-latitudes, while decreases are likely in most subtropical land regions.
GHG emissions have grown since pre-industrial times, with an increase of 70 per cent between 1970 and 2004. Without robust climate change mitigation policies, global GHG emissions will continue to grow over the next few decades.
Potential for Mitigation
Studies indicate that there is a substantial economic potential for mitigation of global GHG emissions over the coming decades, if policies and measures are put into place to remove market barriers.
The IPCC volume on mitigation showed that the largest areas for mitigation potential in countries that have signed the Convention on the Organization for Economic Co-operation and Development are in the energy supply, transport and building sectors. However the IPCC also recognizes that changes in lifestyle and behaviour patterns can contribute to climate change mitigation:
- Changes in lifestyle and consumption patterns that emphasize resource conservation can contribute to developing a low-carbon economy that is both equitable and sustainable.
- Implementation of industry management tools including staff training, reward systems, regular feedback and documentation of existing practices can help overcome industrial organization barriers, reduce energy use and GHG emissions.
During the last ice age, average temperatures were only 5°C cooler than they are today. Considering the extreme impact only a few degrees' difference can have on the planet, the IPCC review of current mitigation policies is highly significant.
The IPCC has released three volumes of its Fourth Assessment Report. The fourth and final volume, the synthesis report, will be released November 16, 2007. That final release will offer an overall scientific view on climate change and pull together the information from the other volumes.
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