10As the world's largest distributed store of freshwater, groundwater plays a central role in 11 sustaining ecosystems and enabling human adaptation to climate variability and change. 12The strategic importance of groundwater to global water and food security will intensify 13 under climate change as more frequent and intense climate extremes (droughts, floods) 14 increase variability in soil moisture and surface water. Here we critically review recent 15 research assessing climate impacts on groundwater through natural and human-induced 16 processes as well as groundwater-driven feedbacks on the climate system.

[1] We review the sea-level and energy budgets together from 1961, using recent and updated estimates of all terms. From 1972 to 2008, the observed sea-level rise (1.8 ± 0.2 mm yr −1 from tide gauges alone and 2.1 ± 0.2 mm yr −1 from a combination of tide gauges and altimeter observations) agrees well with the sum of contributions (1.8 ± 0.4 mm yr −1 ) in magnitude and with both having similar increases in the rate of rise during the period. The largest contributions come from ocean thermal expansion (0.8 mm yr −1 ) and the melting of glaciers and ice caps (0.7 mm yr −1 ), with Greenland and Antarctica contributing about 0.4 mm yr −1 . The cryospheric contributions increase through the period (particularly in the 1990s) but the thermosteric contribution increases less rapidly. We include an improved estimate of aquifer depletion (0.3 mm yr −1 ), partially offsetting the retention of water in dams and giving a total terrestrial storage contribution of −0.1 mm yr −1 . Ocean warming (90% of the total of the Earth's energy increase) continues through to the end of the record, in agreement with continued greenhouse gas forcing. The aerosol forcing, inferred as a residual in the atmospheric energy balance, is estimated as −0.8 ± 0.4 W m −2 for the 1980s and early 1990s. It increases in the late 1990s, as is required for consistency with little surface warming over the last decade. This increase is likely at least partially related to substantial increases in aerosol emissions from developing nations and moderate volcanic activity. Citation: Church, J. A.,

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Removal of water from terrestrial subsurface storage is a natural consequence of groundwater withdrawals, but global depletion is not well characterized. Cumulative groundwater depletion represents a transfer of mass from land to the oceans that contributes to sea‐level rise. Depletion is directly calculated using calibrated groundwater models, analytical approaches, or volumetric budget analyses for multiple aquifer systems. Estimated global groundwater depletion during 1900–2008 totals ∼4,500 km3, equivalent to a sea‐level rise of 12.6 mm (>6% of the total). Furthermore, the rate of groundwater depletion has increased markedly since about 1950, with maximum rates occurring during the most recent period (2000–2008), when it averaged ∼145 km3/yr (equivalent to 0.40 mm/yr of sea‐level rise, or 13% of the reported rate of 3.1 mm/yr during this recent period).