Track 16

Track 16

In today’s talk I’m going to give you an overview of the most recent thinking on climate change. Recently the IGPCC - the Intergovernmental Panel on Climate Change - has conducted a major review of the evidence for climate change.

In its conclusions, it states that the evidence for global warming continues to be overwhelming. However, according to the panel, some of the risk factors identified in earlier reports have been overstated, whereas other impacts of global warming may have been understated.

In this talk, I’m going to outline some of the overstated risk factors and explain the current position on each. I’ll then mention briefly some of the aspects of global warming that are now considered to be a more serious problem than previously thought.

One of the most significant revisions in the new report concerns estimates of rising sea levels. Previous studies had predicted that sea levels would rise by more than two metres. The latest evidence suggests that sea levels are likely to rise by no more than one metre.

This is good news for many coastal areas as flood defences currently in place are much more likely to cope with a rise of one metre. A rise of two metres would have required major investment in flood defences.

The reason climate scientists have come up with such different predictions of sea level rises has to do with our understanding of what is happening to the major glaciers and ice sheets around the world.

Some appear to be contracting faster than predicted, and others appear to be expanding. In 2007, for example, the I6PCC predicted that the Arctic would be ice free in summer by 2080. The latest predictions bring this date forward by 20 years to 2060.

In the Antarctic, on the other hand, the ice sheet appears to be expanding as sea water freezes over. This variability in ice sheet activity accounts for the differences in our predictions of rising sea levels. Another significant revision of our understanding of climate change concerns the Gulf Stream.

As many of you probably know, the Gulf Stream is a current of warm sea water that travels from the tropics northeastwards across the Atlantic. It is responsible for keeping temperatures in Europe and North America 5-10 degrees warmer than they would be otherwise.

An earlier study concluded that the flow rate of the Gulf Stream had decreased by 30 per cent since the 1950s. It warned that the northern hemisphere could be heading for another ice age, in other words, a period of prolonged cold.

However, a more recent study has indicated that currents of warm water have actually accelerated in the last 20 years. Climate scientists now believe that these differences are due to natural variability and that the Gulf Stream is unlikely to disappear.

This is good news for those who live in Europe and North America. I’d like to move on now and mention some of the consequences of global warming and some of the risk factors which may have been underestimated by previous studies.

As far as consequences go, there is new evidence that tropical forests are more susceptible to drought than previously thought and that the severity of severe weather events such as hurricanes and typhoons may have been underestimated in the past. This is particularly bad news for those who live in southern regions.

More worrying, there is stronger evidence that thawing permafrost in northern regions is producing very high emissions of methane gas. As I explained in an earlier lecture, methane is a much more potent greenhouse gas than carbon dioxide.

This thawing ground has the potential to significantly exacerbate climate change. I therefore have to conclude this talk by saying that, in spite of the good news on rising sea levels, global warming continues to be a serious cause for concern. To ignore it would be most irresponsible.