As discussed yesterday, major results from the new report on climate change have been released. This section concerns the scientific basis and conclusions of the assesment; social and political impacts and implications will be addressed later. The conclusions and predictions in the report are clearer and more compelling than ever before, and today’s press release has stirred a lot of controversy. World leaders are also struggling to address it appropriately, and having a bit of trouble.
The Policymaker’s Summary of the Physical Science Basis is a very interesting read. I’d like to highlight some of the report. Before we start, here are a few definitions:
- Very Likely: less than a 10% chance of being wrong
- Likely: less than a 33% chance of being incorrect
- Very High Confidence: at least a 90% chance of being correct
- High Confidence: at least an 80% chance of being correct
Here are the main statements in the summary:
Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years . The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous oxide are primarily due to agriculture.
The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report (TAR), leading to very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, …
Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level.
At continental, regional, and ocean basin scales, numerous long-term changes in climate have been observed. These include changes in Arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy
precipitation, heat waves and the intensity of tropical cyclones (including hurricanes and typhoons).
Paleoclimate information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1300 years. The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to
4 to 6 metres of sea level rise.
Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. This is an advance since the TAR’s conclusion that “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”. Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.
Analysis of climate models together with constraints from observations enables an assessed likely range to be given for climate sensitivity for the first time and provides increased confidence in the understanding of the climate system response to radiative forcing.
For the next two decades a warming of about 0.2°C per decade is projected for a range of SRES emission scenarios. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.
Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.
There is now higher confidence in projected patterns of warming and other regional-scale features, including changes in wind patterns, precipitation, and some aspects of extremes and of ice. Some of these projections include:
- Snow cover and permafrost are projected to be reduced
- Sea ice is projected to shrink in both the Arctic and Antarctic under all SRES scenarios. In some projections, Arctic late-summer sea ice disappears almost entirely by the latter part of the 21st century.
- It is very likely that hot extremes, heat waves, and heavy precipitation events will continue to become more frequent.
- Based on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical SSTs (there is less confidence that there will be more storms) .
- Extra-tropical storm tracks are projected to move poleward, with consequent changes in wind, precipitation, and temperature patterns, continuing the broad pattern of observed trends over the last half-century ( for Atlantic Canada this means more rain and less snow).
- Since the TAR there is an improving understanding of projected patterns of precipitation. Increases in the amount of precipitation are very likely in high-latitudes, while decreases are likely in most subtropical land regions , continuing observed patterns in recent trends.
Anthropogenic warming and sea level rise would continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized.
One of the most interesting aspects of the summary are the figures and graphs at the end, especially the error bars. These indicate unequivocal warming, sea level rise, etc.
For me, the most compelling aspect of the report is that the climate is going to continue to warm up, even if we cap world emissions at the levels of 7 years ago. This means that my nieces and nephews may never see an iceberg pass by St. John’s harbour when they grow up. The ecology will change, fisheries will change regardless of changes in fishing practices, and copying across the pack may only be possible in northern Newfoundland. Much of Newfoundland culture is strongly linked to the sea, the land, and the weather, including things like the family going to the beach for the capelin run, families going out and picking blueberries and bakeapples in season,tobogganning and pond skating in the winter, and freezing your buns off ice-fishing for mud trout.
But the message is clearer and harder to refute than ever before, and with enough pressure the powers that be stubborn may be forced into a positive response.
For some interesting discussion of the news release, check out RealClimate.