BBC’s Question Time on 14 November saw Lord Lawson citing the IPCC findings to support one of his arguments. Did I dream that? Then I realised that, of course, the reference to the IPCC was incomplete and misleading so I knew I was awake and back in the strange media-distorted world of the UK debate on climate change.
According to the Daily Express, Lord Lawson said that “If you look at the inter-governmental panel on climate change they say there is absolutely no connection between climate change and tropical storms.” Wrong, but convenient for someone who argues we probably don’t need to do anything much about climate change.
What the IPCC actually said in the admirably cautious Technical Summary of the Fifth Assessment Report (AR5) was that:
“Globally, there is low confidence in attribution of changes in tropical cyclone activity to human influence. This is due to insufficient observational evidence, lack of physical understanding of the links between anthropogenic drivers of climate and tropical cyclone activity, and the low level of agreement between studies as to the relative importance of internal variability, and anthropogenic and natural forcings.”
So far so good for Lord Lawson, but then, the IPCC goes on to say:
“Projections for the 21st century indicate that it is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged, concurrent with a likely increase in both global mean tropical cyclone maximum wind speed and rain rates (Figure TS.26). The influence of future climate change on tropical cyclones is likely to vary by region, but there is low confidence in region-specific projections. The frequency of the most intense storms will more likely than not increase substantially in some basins. More extreme precipitation near the centers of tropical cyclones making landfall are likely in North and Central America, East Africa, West, East, South and Southeast Asia as well as in Australia and many Pacific islands.” (my emphasis).
In making this statement, the IPCC reflects the fact that, while the science is by no means settled, there are a number of studies that provide physical mechanisms linked to climate change that suggest the frequency of the most intense storms would increase with warming. As I understand it, the warmth of the near surface ocean provides the basic fuel for the cyclone: the winds spiralling around the system evaporate water which cools the ocean and puts latent heat into the atmosphere. When the air rises and the water condenses in deep convection in the storm the heating leads to extra ascent, drawing in more air and leading to faster surface winds. The warmer the ocean is, the more fuel there is for a potential tropical cyclone, and the stronger they could be. Many other aspects come into play such as the changing winds with height and the temperature of the atmosphere up to 15 km. However, in a warmer world, the potential for stronger storms is there.
Indeed, based on this sort of evidence, the quote highlighted above is a statement that the IPCC judges there is more than a 50% chance that the frequency of the most intense storms will increase substantially in some ocean basins. So if Typhoon Haiyan was not affected by climate change and yet was still one of the most powerful storms ever making landfall, it’s clear that the Philippines and other regions exposed to tropical cyclones have a lot to worry about unless we make a “substantial and sustained reductions of greenhouse gas emissions (SPM Section E).” It would be good to see Lord Lawson quoting that particular part of the IPCC AR5 report!