Climate change

In 1896 Swedish physicist Arrhenius asked a new and important question, namely why is the temperature of the Earth so suitable for humans and other forms of life? From that emerged the concept of the greenhouse effect, namely that the concentrations of various atmospheric gases [e.g. carbon dioxide (CO2), methane, nitrous oxide, chlorofluorocarbons; also called greenhouse gasses] was such that some of the radiant heat received from the sun is trapped, rendering the earth a considerably warmer planet than it otherwise would be. Arrhenius even did a manual calculation of the effect of doubling the preindustrial level of CO2. His results are precisely what the supercomputer models of Earth’s climate predict. We are well on the way toward that CO2 concentration, having started at preindustrial levels of 280 ppm (parts per million). Current atmospheric levels are 390 ppm of CO2, and are increasing at a rate above the worst case scenario of the Intergovernmental Panel for Climate Change (IPCC) (Canadell et al. 2007). Modern science is able to study past climate, so we now know that the last 10 000 years were a period of unusual stability in the global climate. This probably has been extremely beneficial to the human species for that period includes all our recorded history as well as the origins of agriculture and of human settlements. It is easy to conclude that the entire human enterprise is based on a freak stretch of relatively unchanging climatic conditions. A bit less obvious is the realization that ecosystems have adjusted to that stable climate also so they – as well as the benefits society receives in ecosystem goods and services (see Chapter 3) – are vulnerable to climate change as well. Indeed, it is rapidly becoming clear that the natural world is as – or more – sensitive to climate than anything else society is concerned about. The current levels of greenhouse gas concentration have already led to an overall rise in global temperature of 0.75 degree Celsius (see Figure 8.1). In addition, because there is a lag between attaining a concentration level and the consequent trapping of heat energy, the planet is slated for an additional 0.5 degree (for a total of 1.25 degrees Celsius) even if greenhouse gas concentrations were to cease to increase immediately. This chapter highlights the effects of humaninducedclimate changeonEarth’sphysical environments and biodiversity. Possible mitigation options of this predicament are also briefly discussed.