The “observation minus reanalysis” (OMR) method has been used to estimate the impact of changes in land use (including urbanization and agricultural practices such as irrigation) by computing the difference between the trends of the surface observations (which reflect all the sources of climate forcing, including surface effects) and the NCEP/NCAR reanalysis (which only contains the forcings influencing the assimilated atmospheric trends). In this paper we apply the OMR method to surface stations in Argentina for the period 1961–2000. In contrast to most other land areas, over most of Argentina there has been net cooling, not warming (about −0.04°C/decade). Observations also show a very strong decrease in the diurnal temperature range north of 40°S. This is associated with an observed strong reduction in the maximum temperature (−0.12°C/decade) together with a weak warming trend in the minimum temperature (0.05°C/decade). The OMR trends show a warming contribution to the mean temperature (+0.07°C/decade) and a decrease in diurnal temperature range (−0.08°C/decade), especially strong in the areas where the observed precipitation has increased the most and where, as a consequence, there has been an exponential increase of soy production in the last decade. The increase in precipitation is apparently associated with an increase in the moisture transport from the Amazons to northern Argentina by the low-level jet.