IPCC Impacts

The IPCC’s second working group, focusing on impacts, risk and adaptations related to climate change, published its segment of the Fifth Assessment Report on Monday in Yokohama Japan.  The report builds on the first working group’s report, published in September, which discussed the state of the science around climate change.  Their conclusion?  The earth is unequivocally warming, the scientific community is 95% certain that it is due to human actions, the impacts of man-made warming are negative for much of the world, and they are only going to get worse.

The last IPCC assessment report was published in 2007 and won the IPCC a Nobel prize.  Since then, the available research on climate change and its impacts has more than doubled.  This gives the IPCC, which integrates research rather than conducting its own, a much larger store of knowledge to draw from.  As a result, this report is the most comprehensive assessment of the impacts of climate change to date and, for the first time, includes an extensive assessment of the risks posed by climate change.  The report also makes explicit how certain the scientific consensus is regarding each of their claims.

While it is worth reviewing the Summary for Policy Makers, we’ll go through the five most important conclusions from the impacts and adaptation sections here.

Beginning with the impact of climate change on biodiversity, the report, despite the recent furor over climate change’s contribution to species extinction, has high confidence that few recent extinctions are the result of climate change.  This is not to say that climate change will not drive future extinctions.  The report has equally high confidence that historic climate fluctuations, which occurred at much slower rates than the present shifts, resulted in significant species extinctions.  Further, climate change has already resulted in changes in many species’ traditional ranges — changes that may result in extinction for species in geographically isolated ecosystems without access to migratory corridors.

Turning to human impacts, the report has high confidence that the negative impacts on farming are more common than positive ones.  In contrast to claims that climate change may be beneficial to agriculture, at least in the short run, the report has high confidence that the positive impacts have been constrained to higher latitudes and even there the impacts are mixed.  There is little evidence that the net global impact has been anything but negative.  In terms of specific crops, wheat and maize have been most negatively affected to date, while soy and rice have been relatively unaffected.  Notably, the largest effect of climate change on agriculture has not been on production but on food security — weakening access to nutrition in already struggling areas of the world.

In broader economic terms the global cost of climate change is likely to be between 0.2% and 2.0% of annual global income.  However, the cost is “more likely than not to be larger, rather than smaller, than that range.”  There is also limited evidence, but high agreement, that costs will vary widely across countries, with some suffering more than the average.  The variation is likely to result in slower regional growth and new forms of poverty traps in developing countries.  The report notes that the social cost of carbon likely ranges between a few dollars and several hundred dollars per ton — a value that is sensitive to the discount rate chosen and the damage functions used, but which is certainly greater than the current price of zero that we collectively place on carbon emission.

All of these economic conclusions should be taken with a grain of salt.  While the authors report that damages accelerate with greater warming, they note that few economic studies look at a world in which warming surpasses 3 degrees Celsius above pre-industrial levels, a level that we are well on pace to surpass by 2080, at which time much of North America and Europe are projected to have seen more than four degrees warming.


As a final note on impacts, the report finds that climate change is likely to simply exacerbate existing health problems.  Much of the direct impact has been in the form of increased vulnerability and death from heat or cold related causes.  However, the broader impacts of climate change on disease vectors and burdens remain under-researched.

Lastly, the report notes that adaptive measures have become more prevalent around the world.  This is true both in terms of actual adaptive measures — sea walls, new building requirements, etc. — and in government and management processes.  As a whole, the world is more aware of climate change and the risks it poses and so is taking action to codify methods to increase adaptive capacity.  Unfortunately, adaptation is likely to be most effective at avoiding short-term impacts.  Dealing with longer-term issues will likely require adaptation in concert with significant mitigation efforts.  However, the report notes that these efforts at adaptation and mitigation often come with substantial co-benefits.  In other words, we should be doing things like clean energy and watershed management anyway.

The newest report has very little good to say about climate change and our response to it.  It underlines the challenge that climate change presents and, while it does mention some positive steps that have been taken, ultimately highlights the fact that the worst is yet to come and we are not prepared.  While vulnerability is dependent on many factors — socioeconomic status and gender in particular — the effects will be felt to some degree or another by everyone.  Hopefully the stark language serves as a call to action that accelerates the positive steps we have already taken.

Image Credit: Phillip Capper via Wikimedia Commons


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