What is the link between global warming and drought?

I’d like to give you a very small selection of references and discussions about the link between global warming and drought.

Global warming probably has two major effects. First, more moisture gets into the atmosphere because warmer air passing over the oceans can take in more water. This can cause more rain and possibly more severe storms and flooding. But the atmospheric system also changes in another way. The hydraulic cycle, as it is called, intensified in both directions, wet and dry. If you live on the East Coast of the US and you move to where I live in the upper Midwest, you’ll get a special appreciation of this. Rain on the East Coast comes in thunderstorms now and then, but a lot of the rain comes from big wet air masses linked to the ocean. In Boston it can rain for a few days off and on but mostly on, with an inch off rain falling over a long period of time. But here in the Midwest, that almost never happens. Instead, it’s not raining, then this big scary storm comes and dumps a whole pile of rain on you, then it moves on. In between storms it can be dry vor many days. The Midwestern storms come from warm air masses passing over the Gulf of Mexico and moving north (then turning “right” at some point) with contributions from elsewhere. It is more intensified hydrological system, with a lot of variation. That is a min-model (albeit a pretty inexact one) for shifting to a warmer planet. Keep in mind that between rain storms, warmer air takes moisture out of the local system (to dump it in a storm somewhere else). Climate experts generally agree that a warmer world will have more severe storms, though which storms will be more severe and in what way is not clear, and drought. Lots of that.

This is actually something that kinda pisses me off by the way. I am an Africanist. I have worked and lived in Africa and I pay attention to Africa. Aridification has been an issue in Africa for decades. This has probably been caused, or worsened, by global warming. When people say “Oh, what will happen with global warming” I get annoyed because the effects of global warming have been occurring for a long time, and in Africa, it has totally disrupted the food supply in many areas and millions of people have died. We are starting to see the effects of drought on the food supply now in North America, but it has been happening elsewhere for quite some time.

And THAT also pisses me off a bit. Global warming denialists say things like “what about the dust bowl, huh? What about the 1930s when it was warm, or what about this or that thing that happened in the 20th century?” The release of fossil carbon into the atmosphere has been going on for a century and a half. Global warming is not a thing that started happening the day after the first Earth Day.

Having said all that, it is also true that there are “natural cycles” of climate. But the fact that there are natural cycles does not mean that global warming does not exist. The normal ups and downs of this or that measure (rainfall, drought, temperature, whatever) happen on a baseline, and that baseline is shifting with global warming.

Anyway, I’ve put together a short list of a few very handy studies or commmentaries on the link between global warming and drought. This is nothing like complete, just a sampling. If I have time I may update it in the future to include more information. I’ve ordered these items roughly by time to give some sense of change over time in understanding the problem.

2005: The water cycle is thought to intensify with global warming, thus drought and flooding would be more common. The empirical evidence supporting the increase in storms and flooding is not strong, but for drought it very suggestive.

One of the more important questions in hydrology is: if the climate warms in the future, will there be an intensification of the water cycle and, if so, the nature of that intensification? There is considerable interest in this question because an intensification of the water cycle may lead to changes in water-resource availability, an increase in the frequency and intensity of tropical storms, floods, and droughts, and an amplification of warming through the water vapor feedback. Empirical evidence for ongoing intensification of the water cycle would provide additional support for the theoretical framework that links intensification with warming. This paper briefly reviews the current state of science regarding historical trends in hydrologic variables, including precipitation, runoff, tropospheric water vapor, soil moisture, glacier mass balance, evaporation, evapotranspiration, and growing season length. Data are often incomplete in spatial and temporal domains and regional analyses are variable and sometimes contradictory; however, the weight of evidence indicates an ongoing intensification of the water cycle. In contrast to these trends, the empirical evidence to date does not consistently support an increase in the frequency or intensity of tropical storms and floods.

Evidence for intensification of the global water cycle: Review and synthesis
Thomas G. Huntington,

2010: Global warming has been causing drought in Africa (Commentary by Jeff Masters):

Global warming theory predicts that although global precipitation should increase in a warmer climate, droughts will also increase in intensity, areal coverage, and frequency (Dai et al., 2004). This occurs because when the normal variability of weather patterns brings a period of dry weather to a region, the increased temperatures due to global warming will intensify drought conditions by causing more evaporation and drying up of vegetation. However, the models used in the 2007 IPCC report on climate change mostly predict an increase in rainfall over the Horn of Africa and the Sahel region of Africa (the southern boundary of the Sahara Desert) by the end of this century (Figure 3). The increased precipitation may act to limit the length and areal extent of droughts in these regions in coming decades. The droughts that do occur may increase in intensity, though, since temperature are predicted to increase by several degrees Centigrade. Could increased rainfall lead to a re-greening of the Sahara towards the lush conditions that existed 12,000 years ago? It is possible, argues Stefan Kropelin of the Institute of Prehistoric Archaeology at the University of Cologne in Germany. Satellite imagery has shown a greening of some southern portions of the Sahara (the Sahel) in recent years, he points out. However, some climate models show lower precipitation in coming decades for the Sahel and Horn of Africa, leading architect Magnus Lasson to propose building a 6,000 km long wall across the Sahara Desert to stop the spread of the desert. The wall would effectively be made by “freezing” the shifting sand dunes, turning them into sandstone using a bacterium called Bacillus pasteurii commonly found in wetlands. The microorganism chemically produces calcite–a kind of natural cement.

2011: Major study concludes that recent warming has caused widespread drying over land.

Characteristics and trends in various forms of the Palmer Drought
Severity Index during 1900–2008

All the four forms of the PDSI show widespread drying over Africa, East and
South Asia, and other areas from 1950 to 2008, and most of this drying is due to recent
warming. The global percentage of dry areas has increased by about 1.74% (of global
land area) per decade from 1950 to 2008. The use of the Penman?Monteith PE and self?calibrating PDSI only slightly reduces the drying trend seen in the original PDSI. The percentages of dry and wet areas over the global land area and six select regions are
anticorrelated (r = ?0.5 to ?0.7), but their long?term trends during the 20th century do
not cancel each other, with the trend for the dry area often predominating over that for the wet area, resulting in upward trends during the 20th century for the areas under extreme (i.e., dry or wet) conditions for the global land as a whole (?1.27% per decade) and the United States, western Europe, Australia, Sahel, East Asia, and southern Africa.
The recent drying trends are qualitatively consistent with other analyses and model
predictions, which suggest more severe drying in the coming decades.

Aiguo Dai. Characteristics and trends in various forms of the Palmer Drought
Severity Index during 1900–2008.

2011: Link between global warming and extreme weather events explored by PBS. See commentary by Stephen Lacey. Video from PBS:

Watch How 2011 Became a ‘Mind-Boggling’ Year of Extreme Weather on PBS. See more from PBS NewsHour.

2011: Dust bowl effect identified as an outcome of global warming and a serious problem for the immediate future.

Commentary by Joe Romm in Nature is summarized here.

2012: Union of Concerned Scientists discusses link between global warming and severe weather.

This pattern of intense rain and snow storms and periods of drought is becoming the new normal in our everyday weather as levels of heat-trapping gases in the atmosphere continue to rise.

2012: Droughts and feared impacts of food supply linked to global warming.

Article by Joe Romm: Brutal Droughts, Worsened By Global Warming, Threaten Food Production Around The World

Severe drought (or Dust-Bowlification) “is the most pressing problem caused by climate change.” As I wrote in the journal Nature last year, “Feeding some 9 billion people by mid-century in the face of a rapidly worsening climate may well be the greatest challenge the human race has ever faced.”…

2012: Public Perception of Climate Change and the New Climate Dice Hansen, J. Sato, M. Ruedy, R. coming out in PNAS, draft here.

“Climate dice”, describing the chance of unusually warm or cool seasons relative to climatology, have become progressively “loaded” in the past 30 years, coincident with rapid global warming. The distribution of seasonal mean temperature anomalies has shifted toward higher temperatures and the range of anomalies has increased. An important change is the emergence of a category of summertime extremely hot outliers, more than three standard deviations (3{\sigma}) warmer than climatology. This hot extreme, which covered much less than 1% of Earth’s surface in the period of climatology, now typically covers about 10% of the land area. It follows that we can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming, because their likelihood in the absence of global warming was exceedingly small. We discuss practical implications of this substantial, growing, climate change.

See also this Op Ed by Hansen.

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10 thoughts on “What is the link between global warming and drought?

  1. “In Boston it can rain for a few days off and on but mostly on, with an inch off rain falling over a long period of time. But here in the Midwest, that almost never happens. Instead, it’s not raining, then this big scary storm comes and dumps a whole pile of rain on you, then it moves on. In between storms it can be dry vor many days.”

    Interestingly, I’ve heard people from the Pacific Northwest and western Europe comment about how sudden and short the rainstorms in Massachusetts are, compared to the weather they’re used to, where it will sometimes drizzle and rain intermittently for days or even weeks. I guess Massachusetts is somewhere in between the climate of the UK or Washington state and that of the Midwest.

    On the serious issue, though, it scares me how quickly the climate seems to be changing, with ice levels declining and extreme weather increasing noticeably over periods of just a few years, which is extremely rapid for worldwide changes. Between climate change and oil and other natural resources peaking and then becoming harder to find, the next century or two will not be easy ones for the human race. I hope we can figure out ways to make it through with human civilization intact.

  2. Yes, I think that’s right. I was just comparing my own experience with coastal weather in Boston with tornado ally.

    Start stocking up now! On what, though, I’m not sure .

  3. You can add dr. Hansen’s latest. He broke the embargo on his paper with an op-Ed inWashPo(?) so the journal has released it early.

  4. I haven’t seen that paper yet. As far as I can tell, there isn’t anything from PNAS in the current issue or their early release.


  5. Hi Greg,
    This is much better than the bald assertion you posted in a previous blog. AGW does not cause drought, floods and wildfire problems, it amplifies them and shifts their geographical location. The US is only now starting to feel the effects. Similar effects in Oz have been noticeable for at least the last decade. The reason that this is a POTENTIAL catastrophe is because those kinds of weather patterns are taking hold in the world’s grain belts (as predicted prior to that by modeling of Hadley cells).

    So called ‘skeptics’ wanted to see observational evidence before doing anything, well here it is. We can put down the extra economic damage done so far as a cost of following their policy path. That cost is being accounted for in actuary tables and has been inflating insurance premiums and grain prices since the turn of the century.

    The time has long past since we need more evidence to justify modernizing our global energy infrastructure. The few powerful Luddites hanging on to their FF’s business model.

    The energy ‘market’ is not a place it’s a set or rules governing trade (not the least of which is property law). Other than political will there is nothing stopping us from tweeking those rules in such a way that the Luddites either adapt their business model or or be eaten by their clean competitors.

    Such tweeks have been made before, eg: the clean air act, the cap and trade treaty for Sulfur emissions instigated by Regan, and the removal of lead from petrol. Each time this sort of tweek happens the same small crowd of Luddites scream like stuck pigs, it’s time to ignore their wolf cries and let our engineers get on with it.

  6. # – The few powerful Luddites hanging on to their FF’s business model.

    Sorry my post is a bit garbled, it was meant to run on with something like “…should be forced to take responsibility for their waste products.”.

  7. John Holdren has violated the Precautionary Princilple by allowing NASA to carsh an SUV into the back yard of Ming The Merciless .

    The irate Emperor might retaliate by firing up the Nitron Ray he used to inflict climate change on the FDR administration.

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