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Halfway to doubling of CO2 radiative forcing
Jorden skinner på jordkloden. Sett fra verdensrommet.We are now halfway to doubling the radiative forcing of CO2 since pre-industrial times, although CO2-concentrations are not halfway to doubling.
Senior scientist Cathrine Lund Myhre, NILU

It is now 50 years since the publication of Syukuro Manabe and Richard Wetherald's classic article, which in many ways marked the start of modern era of climate modeling.

Manabe and Wetherald calculated the effect of several possible drivers of climate change, but especially the effect of doubling CO2. The doubling of atmospheric CO2 concentrations has since become a standard experiment in climate research, and a convenient way of comparing the sensitivity of different climate models.

Gunnar Myhre (CiCERO) and colleagues Cathrine Lund Myhre (NILU), Piers Forster (University of Leeds) and Keith Shine (University of Reading) show that we are now halfway to doubling the radiative forcing of CO2 since pre-industrial times, although concentrations are not halfway to doubling.

Cathrine Lund Myhre states that the global average value of CO2 was 400 parts per million (ppm) in 2015 (WMO), while the global mean value in pre-industrial times was about 278 ppm. The combined radiative forcing from all well-mixed greenhouse gases presently, is 84% of the radiative forcing of a CO2 doubling.

– We estimate that total well-mixed greenhouse gases radiative forcing will be equivalent to a doubling of CO2, with present growth rates, by around 2030, says Gunnar Myhre.

– This is earlier than previous estimates, taking into account the revised stronger radiative forcing of methane, says Cathrine Lund Myhre.

– A recent study (Etminan et al., 2016) published in Geophysical Research Letters provides revised forcing estimates for methane that is 25% higher than in the previous IPCC report.

Read more:

https://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo3036.html

What is radiative forcing?

Radiative forcing is, in very simple terms, the difference between the amount of solar heat that hits the Earth and the amount of heat the Earth reflects back into space.

Radiative forcing is thus used as a measure of the effect a natural or man-made factor has on the climate. (Source: http://klimafakta.origo.no/).

Explained in more detail, radiative forcing (RF) is the basic metric to compare the effect of the various climate change drivers.

RF is the net change in the energy balance of the Earth system due to some imposed change. RF provides a quantitative basis for comparing potential climate response to different changes.

Forcing is often presented as the radiative change from one time-period to another, such as pre-industrial to present-day.

For many forcing agents the RF is an appropriate way to compare the relative importance of their potential climate effect.

References:

Etminan, M., G. Myhre, E. J. Highwood, and K. P. Shine (2016), Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing, Geophys. Res. Lett., 43, 12,614–12,623, doi:10.1002/ 2016GL071930. -
http://onlinelibrary.wiley.com/doi/10.1002/2016GL071930/abstract

Manabe, Syukuro and Wetherald, Richard T., Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity. J. Atmos. Sci. 24, 241-259 (1967)

WMO (2016) Greenhouse Gas Bulletin. The state of greenhouse gases in the atmosphere using global observations through 2015. Geneva, World Meteorological Organization (GHG Bulletin No. 12, 24 October 2016).
URL: http://library.wmo.int/pmb_ged/ghg-bulletin_12_en.pdf

Contact:

Senior scientist Cathrine Lund Myhre, clm@nilu.no

Head of communications Christine F. Solbakken, cfs@nilu.no

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