Understanding Climate Change
Myths and Misinterpretations about Climate Change Due to Human Activities
In the recent preparations and debate concerning the world negotiations on Climate Change, a number of statements have been made in advertisements, editorials, articles and speeches that are scientifically incorrect, or at least misleading. There are many, but some of those arising most frequently are addressed here.
1. Observed Temperature Trends:
The theory and models of enhanced greenhouse gas forcing of climate indicates that temperatures in the upper atmosphere, above clouds, should cool, mid-troposphere layers should warm somewhat and the surface layers, where we live, warm significantly.
1.1 Myth: Observed cooling of the upper atmosphere negates climate change theory.
Fact: It helps confirm both the theory and the conclusion that the changes are now occurring.
1.2 Misinterpretation: The Multi-spectral Scanning Unit (MSU) observations from satellites show a cooling trend since observations began 18 years ago.
Facts: An 18-year period is too short to ascertain trends without adjusting the record for known unusual influences. In addition, combining data from eight different satellites, as was done, introduces errors. The satellite record begins about the time of the longest warm El Nino on record, and moves to the period affected by the temporary cooling of 1992 to 1994 induced by the ash particles from the volcanic eruption of Mount Pinatubo. When these events are taken into account, an underlying warming trend of 0.06 to 0.09ºC is seen. This corresponds well with a 0.1ºC warming over these 18 years for this layer, as observed by conventional balloon soundings.
1.3 Myth: Often cited trends in temperature near the surface are unreliable because observation stations in and near cities show higher temperature than they should because of the growing city "heat island" effect.
Fact: The data sets used to determine global mean warming trends of 0.17ºC in the period of the satellite record, and about 0.5ºC over the past century have been adjusted to remove the well known "heat island" effects.
2. Myth: Global Climate Models (GCMs) are as inherently unreliable as macro-economic models so projections of future climate cannot be trusted.
Fact: There are major differences between climate and economic models:
3. Misinterpretation: Warming would only be about 1.2ºC with a doubled CO2 concentration if the theory and models did not predict an uncertain increase in water vapour (a greenhouse gas) to augment the CO2 effect.
- the former are based on well founded equations derived from fundamental physical laws describing atmospheric circulation and energy exchanges in the atmosphere and between the earth, sun and space. This is unlike econometric models of human and economic behaviour, based on past behaviour, which is constantly changing.
- the GCMs showing climate forced by greenhouse gases and aerosols are tested against observed past climate variations and changes to ensure reliability. For example, once the volume of ash particles from the Mt. Pinatubo eruption was known, the GCMs accurately predicted the temporary cooling effect.
Fact: Models project greater concentration of atmospheric water vapour as the CO2 induced warming proceeds, which causes more evaporation and a warmer atmosphere which holds more water vapour although the magnitude of this effect is still under scientific debate. In the past 30 years statistically significant increases in atmospheric water vapour have been observed over North America and elsewhere, consistent with model predictions and augmenting the CO2 effect.
4. Misinterpretation of Uncertainty: Oceans and vegetation could absorb more CO2 as atmospheric concentrations increase.
Fact: On average over the past decade, about half of the CO2 emissions emitted by human activities are retained in the atmosphere and about half goes into oceans, soils and trees. There is, indeed, uncertainty about whether this will change in futures, but some recent studies suggest that it is more likely that climate changes will result in changed ocean circulations that will reduce CO2 absorption, leaving a greater percentage in the atmosphere to affect climate. Increases in vegetation growth with more CO2 in the air are already taken into account in climate models, but this could be offset by more frequent forest fires not factored into the models.
5. Correct Statement Misinterpreted: Contrary to popular belief tropical cyclones (hurricanes) have not increased, and models do not indicate global increases in frequency and intensity in a warmer climate.
Fact: The observed record and model projections confirm that this is correct. However, the damages and loss of life due to storm surges accompanying tropical cyclones are increasing and will continue to increase with rises in mean sea level in a warming world. Other extreme climatic events such as heavy one-day rainfalls causing floods and intense winter storms are both projected to increase and have already been observed to do so in a number of regions which have reliable records. Climate related disaster losses are rising rapidly, more rapidly than losses due to earthquakes and volcanos.
6. Misinterpretation: The Conference Board of Canada's review of the economic effects of stabilization or 5 to 10 % reductions in emissions indicate that they would be costs 0.5 to 2.3 % of GDP by 2010, giving a small reduction in projected GDP growth of 30% by that time.
Fact: The Conference Board's report reviewed 16 studies of net economic effects in Canada of emission limitations on GDP which ranged from strongly positive to minus 2.3%. The variations depend largely on the assumptions made in the economic models used. The Conference Board chose in its Executive Summary to cite "One possible outcome is" and proceeded to select the most negative one, fed by the most pessimistic assumptions. They did not include in their Summary "Other possible outcomes" which are given in the body of the report and which show negligible or positive impact on GDP. Most economists think that a well chosen set of limitation policies will have negligible net effects, positive or negative on the economy.
None of the models reviewed consider the benefits of reduced fossil fuel use on local air pollution are their contribution to reducing rates of climate change.
