Aerosols and climate - a crash course Marianne T. Lund CICERO Nove Mesto 17/9-15

Observed changes in the climate system

IPCC 2013 We observe changes all across the climate system "Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millenia."

Global mean temperature Global mean temperature anomaly

IPCC 2013 Increasing energy in the climate system  more than 90% of accumuated energy between 1970 and 2010 stored in the oceans Global mean ocean heat content Efficient heat uptake by the global oceans Global mean ocean temperature anomaly Warming also of the deep ocean (below 700 m)

Ice, snow and water Global mean sea level change Arctic summer sea ice extent NH spring snow cover IPCC 2013

Extreme events Wuebbles et al. 2015

What drives the changes?

Perturbing the energy balance Radiative forcing: changes in radiative balance

Natural and anthropogenic contributions "(…) It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. " IPCC 2013

A cocktail of emissions

Warming and cooling contributions CO 2, O 3, N 2 O … OppvarmendeAvkjølende AEROSOLS

Radiative forcing 1750 to 2011 IPCC 2013

Aerosols

Definition Main types of aerosols: Dust Sea salt Sulfate Soot (product of incomplete combutions) Organic carbon Products from biomass burning Nitrate “Aerosols are minute particles suspended in the atmosphere”

Natural and anthropogenic sources Myhre et al. 2013

What do aerosols look like? Heintzenberg et al Aerosol sizes can vary from 1 nm to several 100 um >10 um: giant aerosol < 1 um: fine mode

Atmospheric life cycle Aerosols have short atmospheric lifetime and are not well mixed like CO 2. Their impacts can be strongly localized, but aerosols can also be transported over large distances.

Aerosol distributions Myhre et al Aerosols are everywhere, but the amount and mixture of aerosols can be highly variable.

Aerosol impacts Air quality and visibility Health Climate Atmospheric circulation and precipitation Diffuse radiation and photosynthesis

Air quality Dehli Beijing NY Times 14/2/2015

Aerosol health impacts WHO: “7 million people died - one in eight of total global deaths – as a result of air pollution exposure in 2012.”

Aerosol climate impacts

Absorption and scattering of solar radiation Warming Cooling sulfate dust Sea salt Nitrates Organic carbon Soot (black carbon) Brown carbon (?) More details from Bjørn…

Example: Volcanic sulfate Mt. Pinatubo eruption

Example: soot on snow Soot deposited on snow/ice  absorbs radiation  snow melt  enhanced warming AMAP 2011

Impact on clouds More CCNs  more, but smaller droplets  whiter cloud  increased reflection More CCNs  more, but smaller droplets  longer cloud lifetime Local heating by soot  Cloud burn-off Low level clouds reflect solar radiation  cooling Myhre et al. 2013

Aerosol climate impact Our models struggle to accurately represent aerosols and their impacts  measurements IPCC 2013

How sensitive is the Earth’s climate to a doubling in CO 2 ? The stronger the aerosol effect until present, the higher the climate sensitivity Reducing the uncertainties in aerosol climate forcing is crucial Aerosols Greenhouse gases o

Aerosols as part of the solution? Climate engineering

Summary We observe changes all across the climate system consistent with a warming It is extremely likely that human influence has been the dominant cause of the observed warming the last 60 years Greenhouse gases (CO2) dominant warming impact, but important contributions from aerosols Aerosols come in a number of types, shapes and sizes from numerous sources and have high spatial variability in the atmosphere Aerosols influence climate through absorption and scattering of solar radiation and by making clouds whiter Solving the challenges in aerosol science is a key priority Reducing aerosols = co-benefits for air quality and human health