What does the UN panel really say about climate change?
Sunday, April 3, 2011
Among other things, the panel's WG I report provides very weak support for those claiming total world agricultural output will decline with climate change, even for tropical areas, says this former Guelph crop scientist
by TERRY DAYNARD
I've been intrigued by atmospheric science beginning with my early days in crop physiology research, through to my serving on several national climate change committees. That's why I've read the lengthy analyses issued about every five years by the United Nation's International Panel on Climate Change (IPCC), specifically those of its Working Group I (WG I) on the physical science of climate change.
The most recent report, issued in 2007, is very thorough (nearly 1,000 pages) and takes care to state the level of uncertainty in most statements and predictions. (This is not the IPCC committee, so criticized for errors in recent months.)
The WG I report often differs from what's said in the media. Here's a brief summary:
Atmospheric concentrations of three principal greenhouse gases, carbon dioxide (CO2), nitrous oxide and methane have increased substantially since pre-industrial times, though the methane level (associated with livestock agriculture) has now stabilized.
Average air and ocean surface temperatures have also climbed, though there are some poorly understood anomalies (for example, average temperatures were stable or declined from about 1940 to 1970). These changes cannot really be attributed to changes in sun activity, though solar cycles do have dominant long-term effects, including the certain return of continental glaciers in thousands of years to come. Temperatures are warmer now than they were for the centuries before 1900, and perhaps even above temperatures from the years between 0 and 1000 AD.
Warming has generally been greater at higher latitudes (versus tropical), at nights and in winter. Daily temperature ranges have declined.
A major uncertainty involves changes in cloud cover. Clouds reflect sunlight back into space, causing cooling. Clouds are formed by increases in water vapour content (which occur with warmer temperatures) and by increased concentrations of "aerosol" compounds created by such things as pollution, erosion, ocean surf and volcanoes.
These compounds also increase sunlight reflection, and the WG I admittedly rates its own understanding of the science of aerosols as "low." WG I also says that agriculture increases ground reflection – more light being reflected from bare soil surfaces and from snow-covered fields than from forests.
I find this to be critically important; a one per cent increase in total earth reflection of sunshine will offset the warming caused by a doubling of CO2 levels. Major uncertainty involves El Nino/La Nina fluctuations. El Nino warms areas of the Pacific – about 10 per cent of the global surface – by up to 5 C. This short-term warming effect is equal to decades of climate change. Scientists have problems incorporating El Nino/La Nina into climate models.
The WG I is very cautious in statements about changes in climatic volatility, saying that it will be stormier in some undefined areas and less so in others. Rainfall intensity and amounts will increase in many areas (warmer air holds more water), as will evaporation.
Hence, drought will increase in some places and decrease in others. The number of hurricanes is expected to decline, though the intensity of some may increase; the probability for these predictions is about two chances in three, so far from certain. As for the future Sahel region of Africa (of global interest in discussions about drought), WG I says it can't predict if this region will be wetter or drier.
Climate change will likely mean less ice in Greenland, though not in Antarctica. Melting ice and ocean warming (cold water is denser) will raise sea levels by an estimated 20-40 centimetres by the year 2100. Local changes will depend on whether the land itself is rising (the Hudson Bay floor) or sinking (PEI).
The WG I report emphasizes that its predictions about climate changes are continental in scope and based over many decades. Statements that climate change has meant higher temperatures at location X in year Y are made despite WG I cautions.
The WG I report provides very weak support for those claiming total world agricultural output will decline with climate change, even for tropical areas. In Africa and Latin America, it cautiously projects some areas will get wetter and others drier. Canadian and U.S. agriculture should benefit. South and East Asia and Northern Europe should get more rain while the Mediterranean and the Middle East may be drier.
The WG I report can be found at: www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.htm. BF
Terry Daynard is a former faculty member at the University of Guelph and former
executive vice-president, Ontario Corn Producers' Association