Climate Change Prediction and Related Uncertainties

Prediction of future climate change is solely based on the results of computer climate models simulations. In spite of considerable progress in climate modeling achieved in recent decades, large uncertainties remain in predictions of future climate change. These uncertainties stem from several sources. First, to simulate future climate changes, climate models require scenarios for future concentration of atmospheric greenhouse gases, aerosols, and land-cover changes. The latter, in turn, are based on predictions of economic, demographic, and technological development which are rather uncertain. This is why a set of plausible scenarios for anthropogenic climate forcing is produced based on very different assumptions about future socio-economical development. As an example, the upper and lowest projected CO2 emission at the end of twenty-first century differs by factor of 6 for the latest set of emission scenarios produced by Intergovernmental Panel on Climate Change (Figure 4a). These uncertainties in emission scenarios result in a considerable range of

2000 2020 2040 2060 2080

1000

2100

2000 2020 2040 2060 2080 2100

Figure 4 The range of SRES emission scenarios and corresponding CO2 concentration and globally averaged temperature changes simulated with the earth system model of intermediate complexity CLIMBER-2. (a) Envelope of the SRES CO2 emission scenarios for the next 100 years in Gt C yr_1. (b) Simulated CO2 concentration scenarios corresponding to SRES emission scenarios in ppm. (c) Simulated range of global temperature changes. Dark red area corresponds to the range of emission scenarios with the same climate model parameters. Light red area represents the combined range of uncertainties related to emission scenarios and different climate models. SRES emission scenarios are from http://sres.ciesin.org.

2000 2020 2040 2060 2080 2100 Year

Figure 4 The range of SRES emission scenarios and corresponding CO2 concentration and globally averaged temperature changes simulated with the earth system model of intermediate complexity CLIMBER-2. (a) Envelope of the SRES CO2 emission scenarios for the next 100 years in Gt C yr_1. (b) Simulated CO2 concentration scenarios corresponding to SRES emission scenarios in ppm. (c) Simulated range of global temperature changes. Dark red area corresponds to the range of emission scenarios with the same climate model parameters. Light red area represents the combined range of uncertainties related to emission scenarios and different climate models. SRES emission scenarios are from http://sres.ciesin.org.

uncertainties in the future rise of atmospheric CO2 and global temperature (Figures 4b and 4c).

Another important source of uncertainties in future climate predictions is due to a poor understanding of the radiative properties of atmospheric aerosols. Concentration of several types of aerosol is strongly affected by anthropogenic activity. Among them are sulfate, organic carbon, black carbon (soot), and mineral dust. Some of these aerosols cause cooling, while others cause warming of the Earth's surface. In addition, aerosols affect the optical properties of clouds and hydrological processes in the atmosphere (so-called indirect effect of aerosols). Uncertainties in the direct and indirect effects of aerosols remain very large. Furthermore, unlike the well-mixed greenhouse gases, spatial and temporal aerosol distribution is extremely heterogeneous.

Additional source of uncertainties in future climate predictions arises from the interaction between climate and biosphere. It is still not well understood how natural ecosystems will respond to the combination of climate changes and rise of CO2 concentration. Some modeling results suggest that terrestrial biosphere under global warming conditions can turn from a sink of carbon, as it is the case at present, to a considerable additional source of CO2, hence amplifying global warming. Additional methane release from the northern wetlands could also contribute to the amplification of climate change.

At last, different climate models simulate substantially different responses to the same anthropogenic forcing. The globally averaged equilibrium surface temperature response to the doubling of CO2 concentration is used as a benchmark for the climate model sensitivity to changes of the greenhouse gases concentration. This characteristic, called 'climate sensitivity', falls into the broad range between 1.5 and 4.5 °C for different climate models. The reason for such large differences in the climate sensitivity is primarily attributed to the uncertainties related to climate feedbacks, such as water vapor, cloud, and surface albedo feedbacks. Since it is not known which of the climate models is the most accurate for future climate prediction, the whole range of model results has to be used to assess the possible range of uncertainties. Moreover, a possibility remains that the actual climate change may go above the envelope of current climate model simulations.

Project Earth Conservation

Project Earth Conservation

Get All The Support And Guidance You Need To Be A Success At Helping Save The Earth. This Book Is One Of The Most Valuable Resources In The World When It Comes To How To Recycle to Create a Better Future for Our Children.

Get My Free Ebook


Post a comment