Present Climate

The climate of the earth is always changing, one year differs from other years, one decade differs from other decades, one century differs from other centuries, and so on. Arbitrarily defined periods of climatic averages do not adequately reflect the ever-changing aspects of earth's climate. This variability can arise in several ways: (1) natural external changes, such as changes in volcanic activity or, perhaps, small changes in solar radiation; (2) human activities, such as changes in atmospheric greenhouse gases, changes in atmospheric aerosol loading, and changes in land use; and (3) internal variability of the coupled atmosphere-ocean-land-biosphere system.

While it is sometimes difficult to separate external and internal sources of climate variability in data, simulations with climate models are a helpful tool in identifying the possible "fingerprint" of these various modes of variability in models, and then looking for these "fingerprints" in the data. Modeling studies within CCR are examining the mechanisms of El Nino and the Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Tropical Atlantic Oscillation (TAO) and the Pacific Decadal Oscillation (PDO). Other studies are examining the impact of volcanic and solar activity on climate.

Changes in greenhouse gas concentrations and land cover may have also influence climate in the recent past. Carbon dioxide concentrations have increased by about 40% since pre-industrial time (see future climate). Another study, currently in development, will use coupled earth-system models to examine historic changes in land use in China in relation to regional changes in climate and hydrology. This work will be in collaboration with the Earth Environment Institute, Chinese Academy of Sciences.

An important aspect of modeling the present climate accurately is to improve parameterizations of physical processes in models, and to gain improved understanding of the manner in which these processes operate. Various research projects in CCR are contributing to improved understanding of climate processes involving sea-ice, oceans, vegetation, and clouds.