Climatic effects on chemical weathering are evaluated by correlating v
ariations in solute concentrations and fluxes with temperature, precip
itation, runoff, and evapotranspiration( ET) for a worldwide distribut
ion of sixty-eight watersheds underlain by granitoid rock types. Strea
m solute concentrations are strongly correlated with proportional ET l
oss, and evaporative concentration makes stream solute concentrations
an inappropriate surrogate for chemical weathering. Chemical fluxes ar
e unaffected by ET, and SiO2 and Na weathering fluxes exhibit systemat
ic increases with precipitation, runoff, and temperature. However, war
m and wet watersheds produce anomalously rapid weathering rates. A pro
posed model that provides an improved prediction of weathering rates o
ver climatic extremes is the product of linear precipitation and Arrhe
nius temperature functions. The resulting apparent activation energies
based on SiO2 and Na fluxes are 59.4 and 62.5 kJ . mol(-1), respectiv
ely. The coupling between temperature and precipitation emphasizes the
importance of tropical regions in global silicate weathering fluxes,
and suggests it is not representative to use continental averages for
temperature and precipitation in the weathering rate functions of glob
al carbon cycling and climatic change models. Fluxes of Ii, Ca, and Mg
exhibit no climatic correlation, implying that other processes, such
as ion exchange, nutrient cycling, and variations in lithology, obscur
e any climatic signal. The correlation between yearly variations in pr
ecipitation and solute fluxes within individual watersheds is stronger
than the correlation between precipitation and solute fluxes of water
sheds with different climatic regimes. This underscores the significan
ce of transport-induced variability in controlling stream chemistry, a
nd the importance of distinguishing between short-term and long-term c
limatic trends. No correlation exists between chemical fluxes acid top
ographic relief or the extent of recent glaciation, implying that phys
ical erosion rates do not have a critical influence on chemical weathe
ring rates.