摘要：Abundant evidence indicates that tropospheric specific humidity increases in a warmer
atmosphere, at rates roughly comparable to those at constant relative humidity. While the
implications for the planetary energy budget and global warming are well recognized, it is
the net atmospheric cooling (or surface heating) that controls the hydrologic cycle. Relative
humidity influences this directly through gas-phase radiative transfer, and indirectly by
affecting cloud cover (and its radiative effects) and convective heating. Simple
calculations show that the two indirect impacts are larger than the direct impact by
roughly one and two orders of magnitude respectively. Global or regional relative
humidity changes could therefore have significant indirect impacts on energy and
water cycles, especially by altering deep convection, even if they are too small to
significantly affect global temperature. Studies of climate change should place greater
emphasis on these indirect links, which may not be adequately represented in
models.
