A first-order impact of warming on deserts and drylands is that evapotranspiration increases and thereby reduces plant productivity. Experimental and modeling studies indicate that many plants might respond with increased water-use efficiency due to higher amount of atmospheric CO2, and this could make deserts and dryland ecosystems benefit from GHG increase. Whether this effect might provide greater ecosystem service provision is difficult to assess, since it could be counterbalanced by higher water loss due to warming in some areas, and also because many dry rangeland systems are currently overexploited. Moreover, while warming must be expected in most dry regions of the planet, even the sign of changing precipitation is often uncertain and little is known about expected extreme event frequencies. A key conclusion however is that unchanged conditions are highly unlikely for most regions. Deserts are expected to increase in area due to extended drought periods in the Americas and elsewhere.
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