Cities Exacerbate Climate Warming

Lahouari Bounoua,Kurtis Thome,Joseph Nigro

doi:10.3390/urbansci5010027

Abstract

Urbanization is a complex land transformation not explicitly resolved within large-scale climate models. Long-term timeseries of high-resolution satellite data are essential to characterize urbanization within land surface models and to assess its contribution to surface temperature changes. The potential for additional surface warming from urbanization-induced land use change is investigated and decoupled from that due to change in climate over the continental US using a decadal timescale. We show that, aggregated over the US, the summer mean urban-induced surface temperature increased by 0.15 °C, with a warming of 0.24 °C in cities built in vegetated areas and a cooling of 0.25 °C in cities built in non-vegetated arid areas. This temperature change is comparable in magnitude to the 0.13 °C/decade global warming trend observed over the last 50 years caused by increased CO2. We also show that the effect of urban-induced change on surface temperature is felt above and beyond that of the CO2 effect. Our results suggest that climate mitigation policies must consider urbanization feedback to put a limit on the worldwide mean temperature increase.

Highlights

The world population has grown large relative to the size of Earth, and our need for urban land conversion continues to increase
There is growing need to understand its implications for a broad set of environmental issues including food security, carbon uptake [2,3,4], biodiversity [5], and most importantly, urban surface climate which affects the largest proportion of humans [1,6,7,8]
This work models the decoupling of historical changes in surface temperature due to urbanization-induced land use change from those due to change in climate over the continental US (CONUS)

Summary

Introduction

The world population has grown large relative to the size of Earth, and our need for urban land conversion continues to increase. Kalnay and Cai (2003) [23] estimated the impact of urbanization and other land-use changes on climate by comparing trends in surface temperature recorded by several meteorological stations with those assimilated by the National Center for Environmental Prediction and National Centre for Atmospheric Research -NCEP/NCAR reanalysis (Kistler et al, 2001 [24]) They estimated a mean surface temperature warming rate per century twice as high as that previously determined (Hansen et al, 2001 [25]; Gallo et al, 1999 [26]). Zhou et al (2004) attempted a method, similar to that of Kalnay and Cai (2003) [23], to investigate the impact of urbanization and other land-use changes on climate in China and showed a significant urbanization effect They estimate a mean surface temperature warming of 0.05 ◦C per decade in southeast China. We use Landsat-based ISA from the National Land Cover Dataset (NLCD) [30] and MODIS-derived phenological products [22] within a biophysical land surface model (LSM) to untangle the impact of urbanization-induced land use change on surface temperature from that resulting from natural and GHG-induced change in climate

Materials and Methods

Results & Discussion

Daily mean

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