A new publication in Nature Climate Change puts the brakes on predictions that global warming/climate change may produce continental scale droughts into the late 21st century. For example, NCAR said in 2010: CLIMATE CHANGE: DROUGHT MAY THREATEN MUCH OF GLOBE WITHIN DECADES
Then they had to back down and correct the original, when they found the drought PDSI (Palmer Drought Severity Index) numbers were overestimated by double the amount:
Update – July 3, 2012
This news release has been revised to reflect a miscalculation in the original study that inadvertently resulted when simulations of historical drought were combined with simulations of future drought. The revised maps, below, indicate that drought levels on the Palmer Drought Severity Index may reach -10 in certain regions, whereas the levels reached -20 on the original maps. Similarly, upper-latitude areas become less moist than previously projected. Large portions of the globe are still expected to experience dryness that is extreme if not unprecedented. For many regions, the corrected data show the movement toward drought taking place about three decades slower than originally projected.
Here is what NCAR says the future drought scenario looks like under climate change over the next 80+ years:
In this new study published this week, it seems that the model predictions just aren’t lining up with observations, such as the recently observed greening of Earth and the measurements of evapotranspiration, which may have an embedded methodological artifact and failure to account for how plant stomata have been responding.
Potential evapotranspiration and continental drying
P. C. D. Milly & K. A. Dunne
By various measures (drought area1 and intensity2, climatic aridity index3, and climatic water deficits4), some observational analyses have suggested that much of the Earth’s land has been drying during recent decades, but such drying seems inconsistent with observations of dryland greening and decreasing pan evaporation5. ‘Offline’ analyses of climate-model outputs from anthropogenic climate change (ACC) experiments portend continuation of putative drying through the twenty-first century3, 6, 7, 8, 9, 10, despite an expected increase in global land precipitation9. A ubiquitous increase in estimates of potential evapotranspiration (PET), driven by atmospheric warming11, underlies the drying trends4, 8, 9, 12, but may be a methodological artefact5. Here we show that the PET estimator commonly used (the Penman–Monteith PET13 for either an open-water surface1, 2, 6, 7, 12 or a reference crop3, 4, 8, 9, 11) severely overpredicts the changes in non-water-stressed evapotranspiration computed in the climate models themselves in ACC experiments. This overprediction is partially due to neglect of stomatal conductance reductions commonly induced by increasing atmospheric CO2 concentrations in climate models5. Our findings imply that historical and future tendencies towards continental drying, as characterized by offline-computed runoff, as well as other PET-dependent metrics, may be considerably weaker and less extensive than previously thought.
- Characteristics and trends in various forms of the Palmer Drought Severity Index during 1900–2008. J. Geophys. Res. 116, D12115 (2011 Article
- Little change in global drought over the past 60 years. Nature 491, 435–438 (2012). Article , &
- Expansion of drylands under a warming climate. Atmos. Chem. Phys. 13,10081–10094 (2013). Article &
- Increasing Northern Hemisphere water deficit. Climatic Change 132, 237–249 (2015). &
- On the assessment of aridity with changes in atmospheric CO2. Wat. Resour. Res. 51, 5450–5463 (2015). Article , &
- Modeling the evolution of global drought and projections for the twenty-first century with the Hadley Centre climate model. J. Hydrometeor.7, 1113–1125 (2006). Article , &
- Increasing drought under global warming in observations and models. Nature Clim. Change 3, 52–58 (2012). Article
- Global warming and 21st century drying.Clim. Dyn. 43, 2607–2627 (2014). Article , , &
- Responses of terrestrial aridity to global warming. J. Geophys. Res. Atmos. 119, 7863–7875 (2014). Article &
- Terrestrial aridity and its response to greenhouse warming across CMIP5 climate models. J. Clim. 28, 5583–5600 (2015). Article &
- Scaling potential evapotranspiration with greenhouse warming. J. Climate 27, 1539–1558 (2014). &
- Drought under global warming: a review. WIREs Clim. Change 2, 45–65 (2011). Article
- 1993). Handbook of Hydrology (ed. Maidment, D. R.) Ch. 4 (McGraw-Hill,
- Evaporation from sparse crops—an energy combination theory. Q. J. R. Meteorol. Soc. 111, 839–855 (1985). &
- 1974). Climate and Life (Academic,
- A general framework for understanding the response of the water cycle to global warming over land and ocean.Hydrol. Earth Syst. Sci. 18, 1575–1589 (2014). Article , , &
- Land surface controls on hydroclimatic means and variability. J. Hydrometeor. 13, 1604–1620 (2012). &
- Multimodel assessment of water scarcity under climate change. Proc. Natl Acad. Sci. USA 111, 3245–3250 (2014). Article et al.
- Simulation of the impacts of climate change on runoff and soil moisture in Australian catchments. J. Hydrol. 167,121–147 (1995). , , &
- Global pattern of trends in streamflow and water availability in a changing climate. Nature 438, 347–350 (2005). Article , &
- Unprecedented 21st century drought risk in the American Southwest and Central Plains. Sci. Adv. 1, e1400082 (2015). , &
- A drier future? Science 343, 737–739 (2014). Article &
- Macroscale water fluxes 2. Water and energy supply control of their interannual variability. Wat. Resour. Res. 38, 24-1–24-9 (2002). &
- , , & Crop Evapotranspiration—Guidelines for Computing Crop Water Requirements Irrigation and Drainage Paper 56, 15 (Food and Agricultural Organization of the United Nations, 1998).
h/t to Dr. Richard Betts