Short-lived gases Carbon monoxide (CO) RF = + 0.23 Non-methane volatile organic compounds (NMVOC) (benzene, ethanol, etc) RF = + 0.10 Nitrous oxides (NOx) RF = - 0.15 . Total = + 0.18

Aerosols Sources: 90% are natural (not anthropogenic) Dust storms, vegetation, forest fires, volcanoes, sea salt

Volcanic ash pollen sea salt soot

10% anthropogenic Fossil fuel combustion, burning vegetation, incinerators, smelters, power plants 2010 aerosol pollution obscuring Beijing

Grey: no data Intense reds : finer pieces like smoke or pollution Yellow: big pieces, like dust

Direct and Indirect Effects of Aerosols Direct: aerosols reflect solar radiation back to space BUT depends on color, size, composition……. Some aerosols (soot) are dark and absorb solar radiation Sea salt, dust, volcanic ash

Indirect: aerosols are necessary for cloud formation. Aerosols from pollution create small cloud droplets and reflect more solar radiation than natural aerosols

Exhaust from ships creates clouds (ship tracks) Small droplet sizes

Aerosols (short-lived) Except for black carbon (soot from fossil fuel burning) they are negative forcing agents: Net negative RF = - 0.27 Great uncertainty ! IPCC

Land Use Changes Deforestation 2. Overgrazing Net negative RF = - 0.15 less evaporative cooling less precipitation more CO2 from burning; less CO2 removal by photosynthesis increased albedo 2. Overgrazing Net negative RF = - 0.15 Bolivia

The important numbers! Positive forcings are countered by negative forcings especially due to aerosols and the cloud effects of aerosols.. Uncertainty is due to uncertainty in aerosol effects Anthropogenic: Greenhouse Gases ( + 3 Wm -2) (1.68 due to CO2) Aerosols (uncertainty; - 0.27 Wm -2) Land Use/Cover Changes ( - 0.15 ) Total net anthropogenic forcing = + 2.29 Wm -2 Radiative Forcing at top of atmosphere relative to 1750.

GCMs General Circulation Models or Global Climate Models Modeling groups worldwide have developed GCMs IPCC assesses impacts of projected increases in gg and consequences for 21st Century

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Models have become increasingly sophisticated since first IPCC report in 1990 New models use range of gg emission scenarios (RCPs : Representative Concentration Pathways) GG concentration trajectories; represent a range of climate outcomes Research takes place in many countries, and RCPs provide a common, agreed foundation for modelling climate change. The data sets are used to initialize models so that everyone starts from a place everyone else understands, using values everyone is familiar with. RCPs reduce duplication and save money; climate modelling is an expensive business.

RCPs Consider: Radiative forcing at top of atmosphere in 2100 emission rates - how fast we put more greenhouse gases into the atmosphere. emission concentrations, measured in ppm for each gg

RCPs used in Fifth report (2013): 2100 RF relative to 1750 RCP2.6 2.6 RF peaks and declines RCP4.5 4.5 RF stabilizes by 2100 RCP6.0 6.0 RF doesn’t peak by 2100 RCP8.5 8.5

What the models tell us: Temperature Water Cycle Ocean Cryosphere Sea Level Carbon Cycle Climate Change Stabilization, Commitment and Irreversibility

A. Temperature Global surface temperature change by 2100: exceed +1.5°C (relative to 1850 – 1900) Warming will continue beyond 2100 Warming will still show variability and will not be regionally uniform WHAT’S THE BIG DEAL ABOUT 1.5 DEGREES??? “A one-degree global change is significant because it takes a vast amount of heat to warm all the oceans, atmosphere, and land by that much. In the past, a one- to two-degree drop was all it took to plunge the Earth into the Little Ice Age. A five-degree drop was enough to bury a large part of North America under a towering mass of ice 20,000 years ago”.

Increase of global mean surface temperatures for 2081–2100 (late 21st Century) relative to 1986–2005 is projected to be: 0.3°C to 1.7°C 1.1°C to 2.6°C 1.4°C to 3.1°C 2.6°C to 4.8°C Different RCPs

6. Arctic region will warm more rapidly than the global mean warming over land greater than over the ocean 8. more frequent hot and fewer cold temperature extremes over most land areas 9. heat waves will occur with a higher frequency and duration. IPCC