Expert Spotlight: Bill Hare, Climate Analytics

• May 3, 2012

Bill Hare, Climate Analytics

Every so often, the TckTckTck team interviews one of the thought leaders and scientific experts whose work defines our movement. This week we are pleased to share an interview with Climate Analytics Director Bill Hare who took the time to answer our questions about  the scientific connections between climate change and extreme weather and what world regions are most at risk.

TCK: 350.org is leading a global day of action on May 5th – Climate Impacts Day – to help connect the dots between climate change and extreme weather.  What stands out in the recent IPCC report on the subject to help us better understand these connections?  

BILL HARE:think whatstands out is the increasing evidence that some extremes have changed as a result of human influences on climate change, including extreme daily temperatures, such as heatwaves,  extreme precipitation events and coastal high water extremes. Another thing that stands out for me is the relative scale of losses suffered by small vulnerable countries, particularly the small island developing states where losses due to extreme events have exceeded 1% of GDP in many cases and in some cases 8% of GDP. This is an indication of the scale of likely problems in the future.

TCK: The IPCC report lays out potential impacts in levels of confidence. For example: “It is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures at the global scale. There is medium confidence that anthropogenic influences have contributed to intensification of extreme precipitation at the global scale.” What does this mean in practice?

BILL HARE: Scientists can never be absolutely certain about anything really and in science is really important to try and understand what you don’t know and how significant the areas. The IPCC has developed a way of describing uncertainties that he hopes translate into what policymakers an ordinary people can understand, whilst at the same time being rigourous scientifically. In this context, likely simply means that there is a greater than 66% chance that the observed changes in extreme daily and maximum and minimum temperatures have been significantly influenced or caused by human induced warming of the climate system. For most of us, likely is a very good bet that this is the way things really are. The term medium confidence is a way of trying to qualify our knowledge about the extent of human influences on extreme precipitation. We don’t have very high confidence that the observedchanges in extreme precipitation are attributable to human induced warming, but we are modestly sure that this is the case.

The phrase “have contributed to intensification” means that global warming has likely added to the intensity of extreme precipitation events – whilst no particular single extreme event can be attributed to anthropogenic influences the likelihood of such extreme events occurring has changed due to anthropogenic influences.

TCK: What parts of the world should we be most worried about?

BILL HARE: If one looks at where people and human systems are most vulnerable to projected increases in extremes then one does not have to look much further than the small island states and much of Sahelian and sub Sahelian Africa.  This is where people are likely to suffer the most in terms of real human misery and potential loss of life and damages to future development prospects. There are other places to worry about as well-look at what has happened in south-eastern Australia the last years with extreme floods and some tragic loss of life and livelihoods. An increase inintensity of extreme events can sooner or later affect all of our lives, it is just a matter of timing and scale.

The vulnerability in these regions is driven by an unfortunate combination of high exposure and lack of adaptive capacity.

TCK: Some areas of research are described as “low confidence”, like that we’re seeing long-term increases in tropical cyclone activity (intensity, frequency, duration, etc). Is it safe to assume that ”low confidence” is the same as low risk?

BILL HARE: I think a low confidence statement is not meant to convey a sense of low risk. Scientists often defined risks as probability of an event times consequence. A low probability event with a high consequence (such as the disintegration of an ice sheet raising sea level by several metres in a century or so) can still have a high risk. One needs to look at the context carefully and at the underlying science to try and evaluate whether or not the really is a significant risk. I think one thing that is relatively clear arise in the tropical cyclone activity, is that it seems likely that the intensity of the most extreme tropical  cyclones will increase in the future as sea surface temperature rises. Even if there is is an overall reduction in the frequency of tropical cyclones, one must remember that it is the most intense tropical cyclones that cause the most damage, by a wide margin.


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