Drought Indices, Drought Impacts, CO2, and Warming: a Historical and Geologic Perspective
Purpose of Review
Different types of methods give very conflicting impressions about whether water will become scarcer on land as Earth warms, and in what sense(s). Here, I examine how environmental records from past climate changes can be used to clarify the interpretation of these confusing results.
Evidence from the last ice age and the historical era agrees that CO2-driven warming causes a runoff response dominated by regional signals of varying sign, and a vegetation response dominated by greening. This result supports comprehensive Earth system model output, while casting doubt on the interpretation of temperature-driven indices that project widespread “drying” with warming. In contrast, evidence from pre-Quaternary warm climates points to exotic features such as wet subtropics and extremely polar-amplified warming which are not found in model simulations, suggesting unknown forcings and/or feedbacks.
The terrestrial eco-hydrologic response to CO2-driven warming in the recent past is consistent with comprehensive models, and not with drought indices. However, in the deeper past, it is consistent with neither.
KeywordsClimate change Drought Paleoclimate Water cycle Vegetation Runoff
The author thanks Qiang Fu and Brian Soden for the invitation, and also thanks David Battisti, Alexis Berg, Natalie Burls, Ben Cook, Ed Cook, Aiguo Dai, Alexey Fedorov, Qiang Fu, Sandy Harrison, Tim Herbert, Justin Mankin, Chris Milly, Michael Roderick, Jeremy Caves Rugenstein, Christopher Scotese, Richard Seager, Sonia Seneviratne, Abby Swann, and Park Williams for conversations that contributed to the framing and focus of this review.
Compliance with Ethical Standards
Conflict of Interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance
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