LECTURE 1: INTRODUCTION AND GENERAL PRINCIPLES Key Questions: - 1) Is climate changing and is it due to humans? - 2) What will happen next? - 3) What does that mean for us? - Very few scientists doubt that the climate is changing. - There is a need to assess how climate is changing in the future, how can we predict the future, and what are the uncertainties? - There uncertainties based around societal response to climate change. - There is an increasing statistical likelihood that global warming is due to humans - due to anthropogenic emissions of greenhouse gases. IPCC's views on Human impact on climate change: - Third Assessment report (2001): "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations" (66-100%) - Fourth Assessment report (2007): "most of the observed increase in global average temperatures since the mid20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations" (90-100%) - Fifth Assessment report (2013): "Human influence on the climate system is clear" NORTHERN HEMISPHERE - "Its is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th Century" (95-100%) 0.5 0.0 What is happening now? Departures in temperature (C) from the 1961 to 1990 average -0.5 - The Hockey stick curve is an 'icon' of global warming, it is significant as it shows how humans are changing climate. - Current data is compared to a climate baseline (an average of 1960-1990). -1.0 Data from thermometers (red) and from tree rings, corals, ice cores and historical records (blue). 1000 1200 1400 1600 1800 2000 - Proxy data are used, such as tree rings which provide great levels of histories. Year Carbon Dioxide Variations - In previous interglacials, CO2 is never above 300 ppm. 400 400 350 - Since Petit et al 1999 published his graph, CO2 has now risen above 400 ppm. The Industrial Revolution Has Caused A Dramatic Rise in CO 300 350 - One could argue that there is no real other climate forcing responsible for this increase. 1000 1200 1400 1600 1800 2000 Year (AD) CO2 Concentration (ppmv) 300 - CO 2 fluctuates massively, with peaks observed during interglacials and troughs during glacials. Ice Age Cycles 250 - Ice cores are useful over long-term period. - Volcanic eruptions should be causing cooling at present day. 1200 - Scale used on graph - the amount of energy that 1m2 of the earth's is receiving. 400 300 200 100 0 Thousands of Years Ago - More sunspots means more energy and more warming. Year 1400 1000 1200 1600 1800 2000 0.5 Petit et al., 1999 0 What might happen next? Volcanic forcing (W m2) -0.5 a Volcanic forcing TAR -1 - There is projected warming AR4 AIB 0.5 FAR SAR - Global warming of possibly 4 degrees. Solar irradiance forcing (W m") 0.5 b Solar irradiance forcing 1.5 - Some argue that there