Climate, paleoclimate, huevos rancheros, and general asymmetry

On water, climate change, Lomborg, and getting your facts right

with 2 comments

Via John Fleck, I found this opinion piece by Bjorn Lomborg on climate change, water, and adaptation in Bangladesh.  The main thrust of the article is that if the goal is to reduce the harmful consequences of anthropogenic climate change, resources would be better spent on projects to improve access to the basic necessities of the poor and the developing world in general, rather than on reducing carbon emissions.

Not that it should matter what I think, but in this instance I would agree.  I think that improving basic access to clean water, sanitation, health care and nutrition, and infrastructure in the developing world addresses a host of interrelated ethical and moral, social, economic, public health, energy, national security, and environmental issues.  I think such resources would be well-spent and substantially enhance the adaptive capacity of countries in the face of future climate change.  This is not an either/or proposition, however, — the sense one inevitably gets from Lomborg’s writing and those that subscribe to his particular tactics and approach — increasing adaptive capacity, reducing vulnerability, and reducing emission have to proceed together.  There is no one single solution nor policy that addresses the myriad current and future challenges that human populations will face from anthropogenic climate change.

So far, so good.  But then Lomborg writes the following rather incredible sentence,

Cutting carbon emissions will likely increase water scarcity, because global warming is expected to increase average rainfall levels around the world.

There is a technical term for this type of statement.  Dangerously misleading. And it is misleading in important ways that conceal one of the very real and likely imminent challenges we face as a consequence of anthropogenic climate change and is directly relevant to policy.  I’ll maintain that if you get the science wrong, you reduce your chances of developing effective adaptation and mitigation policies.

Consider the Intergovernmental Panel on Climate Change‘s Fourth Assessement Report (AR4).  Figure 3.3 from the IPCC AR4 Synthesis Report shows the precipitation predictions from the multi-model averages based on the SRES A1B scenario — what this means is that it is the average result of over 20 different climate models running one of the mid-range emissions scenarios.


Figure 3.3. Relative changes in precipitation (in percent) for the period 2090-2099, relative to 1980-1999. Values are multi-model averages based on the SRES A1B scenario for December to February (left) and June to August (right). White areas are where less than 66% of the models agree in the sign of the change and stippled areas are where more than 90% of the models agree in the sign of the change. {WGI Figure 10.9, SPM}

Warm colors indicate drier conditions by 2099, cooler colors are wetter. The left panel is December through February, while the right panel is Northern Hemisphere summer.

What immediately jumps out at you will be the spatial patterns.  Regions in the subtropics, including parts of the southwestern United States and much of Mexico and Central America, southern South America, North Africa and the Mediterranean, parts of southwest Asia, and south Africa and Australia show future dry conditions, while the equatorial tropics and the high latitudes get wetter.  There are also important seasonal patterns. South and southeast Asia (from where Lomborg  reports for the Wall Street Journal), for instance, show a drier future dry season and a wetter monsoon season. The Amazon is projected to have a dry June-August, but wetter although less change in boreal winter.

Finally, notice the stippling.  Whereas areas with colored shading indicate 66% of the models agree on the sign (not magnitude) of the change, stippling indicates where 90% of the models agree on the sign.  Two of the most robust projections of the model are the high latitude increase in precipitation, and the extratropical drying.  Note that there is less model certainty in the monsoon region, the setting of Lomborg’s opinion piece.

This latter phenomenon is a robust projection of the suite of global climate models now available, and is colloquially known by climatologists as ‘the rich get richer, the poor get poorer‘ — that is, wet tropical and high latitude areas get more rain, already semi arid regions receive less in the future.

Let’s return to Lomborg’s statement then that,

Cutting carbon emissions will likely increase water scarcity, because global warming is expected to increase average rainfall levels around the world.

In fact, some of the most vulnerable regions of the world will experience severe reductions in precipitation as a consequence of carbon emissions.  Lomborg’s statement is partially backwards and partially not useful — not cutting carbon emission will likely increase water scarcity (in some important regions!), and moreover is likely to do so in the places least likely to be able to adapt to these changes.  This isn’t a statement from me of a preference for adaptation or mitigation (both are needed), this is a situation where not understanding or misstating the science could lead to the wrong policy prescriptions.

Returning to monsoon Asia — the setting of Lomborg’s exhortation for adaptation set in contrast to the efficacy of emissions reduction — uncertainty about the future course of the onset, strength, and intensity of the monsoon still reigns.  While the AR4 models above suggest wetter summer monsoons (but dry winter monsoons), there is less certainty and more spatial variability.  And regional climate models potentially give a different picture.  Recently, researchers from Purdue University found that, in their climate model experiments,  anthropogenic climate change ‘resulted in overall suppression of summer precipitation, a delay in monsoon onset, and an increase in the occurrence of monsoon break periods’

These maps show projected future changes in South Asian summer precipitation and monsoon onset date. A Purdue-led team found that rising future temperatures could lead to less rain and a delay in the start of monsoon season by up to 15 days by the end of the 21st century. (Diffenbaugh lab image) A publication-quality image is available at

So, robust projections from climate models project future subtropical drying, including many areas with considerable vulnerability to climate change and water scarcity.  For other regions, including monsoon Asia, uncertainty is still high.

I maintain that science matters for making sensible climate policy.  If you get the science wrong, you might still accidentally stumble your way into good climate change policy, but adaptation and mitigation policies are more likely to be successful if they address accurately the most likely sources of vulnerability (fundamentals, like will a region get wetter or drier?).  Therefore, undermining or mischaracterizing science in the name of one’s own ideological or policy goals seems likely to, in fact, undermine the chances of success of prescriptions for dealing with the consequences of anthropogenic climate change.  Clean drinking water, sanitation, access to health care — all of these and more are good things irrespective of future climate change.  The scientific details — in space and time and the sign and magnitude of uncertainty — matter, and no one is served well by getting them wrong.

UPDATE: I see Daniel Collins was thinking along similar lines.

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Written by delayedoscillator

November 12, 2009 at 3:49 pm

2 Responses

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  1. [...] of climate science can be exhausting, thankless work, so it’s nice to see delayed.oscillator obliterating his latest. Although I rather doubt anti-regulation propaganda organs like the op-ed section of the WSJ will [...]

  2. Good stuff.


    November 12, 2009 at 8:52 pm

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