Why is the global temperature not increasing more rapidly?

Lennart BengtssonISSIESSC

Why is the global temperature not increasing more rapidly?

• The total effect of greenhouse gas emission on the global radiation balance since 1900 is equal to ca 2.5W/m2.

• This corresponds to a 70% increase of CO2 as the effect is proportional to the logarithm of the concentration.

• At the same time the surface of the global oceans have warmed ca 0.6°C

• Over land areas the warming is about 0.1°C higher

The evolution of global warming

• The warming in time is irregular with a rapid warming 1920-1945, then a minor cooling 1945 -1975 followed by a steep warming 1975-2000.

• After 2000 there has not been any further warming.

• In the same way the warming varies geographically with the highest warming at high latitudes of the Northern Hemisphere but in fact a minor cooling around Antarctica.

What is the general view communicated to the public

• The situation with climate warming is becoming more serious and is in fact much worse than was reported in the IPCC report from 2007.

• Artic ice is melting more rapidly then expected

• The expected losses of the land ices might lead to a rise in sea level by about 1m at the end of this century.

• There will be more cyclones in the future and they will be more intense.

What do we actually observe?

• During the last 5 years the sea level is rising more slowly and the expansion of sea water only contribute some 20%, the rest is melt water and net water transport from land.

• The global surface temperature has stayed more or less constant the last 10 years.

• While sea ice in the Arctic has diminished markedly but the sea ice around Antarctica has been increasing during the last three decades.

• Recent studies have shown that the increase in tropical cyclones in the Atlantic is rather a consequence of better observations.

• Mid latitude storms has not increased in intensity and are not increasing in number.

Surface temperature 1850-2009

Global temperature change

• The surface temperature of the Earth has never been constant, but has undergone changes, sometimes rapid, on a multitude of time scales, many of which are incompletely understood. Since 1900, the global mean surface temperature has increased by 0.6 to 0.8 °C. The warming has not been regular, but has rather occurred in steps that might be interpreted as multi-decadal fluctuations superimposed on a long-term warming trend.

• What is the picture during the last 30 years?• Let us inspect satellite micro wave measurements now

covering 30 years.

Observed temperature trend for the lower troposphere 1979-2008

Temperature of the lower troposphere, TLT, from MSU

• TLT represent the temperature between the surface and ca. 7 km above the ground, most of the radiation comes from the area below 3 km.

• The marked warming peak is related to the El Nino event 1997/98

Observed temperature trend for the lower troposphere 1979-2008

Note the larger warming at higher latitudes of the Northern Hemisphere where climate forcing is

smallest (reflecting aerosols that are less common at the Southern Hemisphere).

Observed trend (+0.149 C/decade) of tropical lower troposphere 1979-2008 (top)

Maximum 30-year trend (+0.220 C/decade) occurring by chance in a 500 year simulation

(below)

Arctic Sea ice 6.5. 2009 mean ice cover 1979-2000 indicated

Antarctic Sea ice 6.5. 2009mean ice cover 1979-2000 indicated

Change in Arctic summer sea-ice 1979-2007

Change in Antarctic “ late summer” sea-ice 1979-2007

What we need to know better

• To what extend are observed changes due to natural processes?

• What are the mechanisms behind the natural processes?

• Could it be that the changes are due to albedo changes caused my anthropogenic aerosol emission?

• In the 1950s and 1960s there was a rapid increase in sulphate aerosols emission due to the industrialization and increasing energy production.

• Presently, the second wave of industrialization dominated by China and India could be the cause of the present reduced warming

The global temperature1850-2008

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* Note minor cooling

Ranking of the global warmest years 1850-2008

OBS

Ökningen av växthusgaser och aerosoler leder till en ändring i jordens energibalans. Hur kan detta beräknas? Hur tillförlitliga är dessa beräkningar? Hur mycket kan

de förbättras?

• Under de senaste 50 åren har jordens värmebalans ändrats med ca 1.8 W/m2. Detta motsvarar en ändring av solarkonstanten med ca 10 W/m2. Detta har i detalj beräknats och också till dels observerats från satellit.

• Detta är 10 ggr mer än solens 11-års cykel

• Effekten av aerosoler har med säkerhet reducerat denna uppvärmning men kan inte tillförlitligt beräknas.

Radiative effects from anthropogenic greenhouse gases.

Radiative forcing of climate 1750-2005 (IPCC, 2007)

Atmospheric feedbacks

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