1. We developed a method to estimate the impact of land-use change (including urbanization and agriculture) on surface temperatures We compare the surface observations with the NCEP 50 year Reanalysis, which is insensitive to land-use change Obtained that the impact of land-use changes is comparable in magnitude to that of greenhouse gases. Impact of urbanization and land-use on climate change Eugenia Kalnay and Ming Cai (Nature, 2003)

2. Issues: The two most important anthropogenic activities that impact climate: 1.increase of greenhouse gases 2.changes in land use They both tend to produce surface warming so that their impacts are very difficult to separate. The impacts of changes in land use have been regarded as “noise”, compared to impacts of increase of greenhouse gases.

3. 1950’s: T ob -T an =0.0 1960’s: T ob -T an =0.61 1970’s: T ob -T an =0.60 1980’s: T ob -T an =0.80 1990’s: T ob -T an =1.40 Example: Baltimore City, MD With time, the observations (in red) become warmer than the reanalysis (in blue). We attribute the difference in the trends, at least partially, to urbanization and other land-use changes.

4. OBS REANAL OBS - REANAL and attribute the difference to land-use changes We do it for each station

5. Land-use changes over the US explain: About 40% of the observed increase in Tmin Most of the observed decrease in Tmax Half of the decrease in diurnal temperature range (-0.14 out of –0.28 C/decade)