Impact of 4 Degree Celsius Warming

Downscaled Global Climate Models (GCMs) projections across three different greenhouse gas emissions scenarios (SRES A2, A1b, B1), all downscaled to a 0.5 degree resolution (~50 km) for the time periods of 1961-1999, 2046-2045, and 2071-2100 show the likely trajectory the climate is likely to take in the coming decades. From different types of climate analyses, we can predict how much more often extreme events, such as droughts and flooding, will occur in the future.

The projected mean temperature and rainfall (from the World Bank Climate Change Knowledge Portal Website, http://sdwebx.worldbank.org/climateportal/index.cfm) for the period 2046-2065 and 2081-2100 (A2 emissions) is shown in the following panels.

These temperature and precipitation projections form the basis of climate metrics and impact modeling results on agriculture, water supply, fire risks, human health, urban energy demand, biodiversity, etc., which can be used to support climate planning and action. The results are not reproduced here due to space limitation. However, suffice it to say that both temperature-based derivative metrics (e.g., average high and low temperature; hottest and coldest temperature; hot days temperature; number of frost days; number of warm days and nights; number of cold days and nights; heat wave duration index; growing degree days; heating degree days; and cooling degree days) and precipitation-based derivative metrics (i.e., total precipitation; consecutive dry days; number of dry periods; number of wet days; wet days; wet day rainfall; 5 day rainfall; and daily rainfall) calculated from daily downscaled future climate projections are robust and have applications in planning crop productivity, water supply, human health, energy demand, and ecosystem resilience in a changing climate. This resource, among others, must be used to inform local and national decision making processes about which policies or specific measures are needed to tackle climate impacts.

Naturally, future climate change analysis is more complicated than it is for the past because there is not a single, but many sets of time series projections from different GCMs runs with a range of CO₂ emissions scenarios. For example, using ensemble analysis to combine the analysis of multiple GCMs and quantify the range of possibilities for future climate under just one emission (A2) scenario, we develop the following climate model maps of ensemble average for change in temperature and precipitation in 2046-2065 and 2081-2100.

These ensembles of climate models tell a story; mean temperatures will increase while annual precipitation will decline. But, this is not futuristic; the impacts of a changing climate are already being felt, with more frequent droughts and more floods, which are forecast to increase with further climate change. This, according to the World Development Report 2010, “is taxing individuals, firms, and governments, drawing resources away from development … continuing climate change, at current rates, will pose increasingly severe challenges to development.” The WD Report further notes that “even relatively modest additional warming will require big adjustments to the way development policy is designed and implemented,…. changing the kinds of risks people prepare for; where they live; what they eat; and the way they design, develop, and manage agro-ecological and urban systems”.

It is very important for Zimbabwe, the Southern Africa region, and Africa to act now, act together and act differently. The imperative of acting now is because of the tremendous inertia in both climate and socioeconomic systems: today’s actions will determine tomorrow’s options; .act together to keep costs down , to protect the most vulnerable and to ensure adequate food and water for all countries; and act differently to transform energy, food production and risk management systems. By acting now, acting together and acting differently, Zimbabwe and Africa will be able to transition to a low emission, climate resilient development path, as well as contribute to stabilizing concentration of greenhouse gases.