Anthropocene physical basis of climate spring 2011 Introduction and UNEP reports Observations Emissions and other natural forcings Temperature record, SSTs Precipitation, Sea level, ENSO, Severe storms Attribution Models and predictions Uncertainties

Svante Arrhenius (1859 -1927) Swedish 1884 PhD dissertation electro-chemistry – did not impress advisor, 150 pages, 85 theses. 1896 – Suggested that CO2 could warm the planet, from his work on ice ages. Emission of CO2 may prevent future ice ages. 1903 – Nobel prize in chemistry for work in his dissertation. Most of his these would be unquestioned today

Intergovernmental panel on climate change (IPCC) Established by WMO and UNEP and confirmed by UN general assembly December 1988 Five reports issued, the latest in 2013 1990 human emissions are increasing atmospheric greenhouse gases, resulting increase 0.3 °C per decade 21st century. 1995 discernible human influence on global climate 2001 surface temperature projected to increase 1.4 - 5.8 C 1990 -2100, and sea level to rise by 0.1 - 0.9 meters 2007 (Nobel peace prize) Climate warming unequivocal. Most increase in global temperatures since mid-20th century is (>90%) due to increase in anthropogenic greenhouse gas concentrations. The fifth one is underway. 831 authors selected from 3000 nominations. 3-4 reviewers for each chapter.

Human activities have changed the composition of the atmosphere since the pre- industrial era Watt’s steam engine Begin industrial period

Global mean surface temperatures have increased

Precipitation patterns have changed Annual mean precipitation change: 2071 to 2100 Relative to 1990

Climate-induced increases in sea level are caused by thermal expansion of the oceans and melting of land ice and ice sheets

Sea Levels have risen

El Niño years La Niña years The frequency, persistence and magnitude of El-Nino events have increased in the last 20 years El Niño years La Niña years The El-Nino phenomena leads to floods and droughts throughout the tropics and subtropics

Weather-related economic damages have increased

Most of the observed warming in the past 50 years is attributable to human activities

Humans are perturbing the carbon cycle Atmosphere The KP seeks to reduce total emissions by about 0.2 This is the “greenhouse” problem 3.3 750 62.3 Estimated Fossil Deposits 6.3 About 16,000 Humans are perturbing the carbon cycle 60 1.6 Plants Driven by fossil fuel emissions 500 Soil 92.3 90 2000 …and land clearing Oceans 39,000 Units Gt C for stores & Gt C y-1 for fluxes The oceans and land vegetation are currently taking up 4.6 Gt C per year

There are fast and slow processes in the carbon cycle

More adverse than beneficial impacts on biological and socioeconomic systems are projected

Land areas are projected to warm more than the oceans with the greatest warming at high latitudes Annual mean temperature change, 2071 to 2100 relative to 1990: Global Average in 2085 = 3.1oC

Annual mean precipitation change: 2071 to 2100 Relative to 1990 Some areas are projected to become wetter, others drier with an overall increase projected Annual mean precipitation change: 2071 to 2100 Relative to 1990

Initially increased agricultural productivity in some mid-latitude regions & reduction in the tropics and sub-tropics even with warming of a few degrees 2020s 2050s 2080s

Uncertainties Changes in atmospheric water vapor Changes in cloudiness Changes in albedo Aerosol particles Direct effects Impact on clouds Black carbon