FAQ 7.1 | How Do Clouds Affect Climate and Climate Change? 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    Clouds can have both warming (by absorbing Earth’s outgoing longwave radiation) and cooling (by reflecting incoming shortwave solar radiation) radiative effects on climate. Depending on its altitude and latitude, cloud can have net warming or cooling effect (Figure FAQ7.1, above). For example, deep, thick clouds in tropical areas have large poisitive longwave radiative effect (warming), while optically thick clouds anywhere will produce negative shortwave radiative effect (cooling). These cloud radiative effects get more complex and dynamic when clouds have rapid adjustments or feedbacks to the warming climate.

 

    Other than radiative effects, when clouds precipitate in forms of rain or snow etc., the surrounding atmosphere will be warmed up due to release of latent heat. Furthermore, convective clouds produce very strong updrafts, which can carry energy, momentum, moisture, aerosols and other chemical atmospheric constituents (e.g. greenhouse gases) and transport them to higher altitude or faraway regions (e.g. from tropics to polar regions).

 

    Currently, cloud feedback parameterization is associated with the greatest inter-model spread in climate sensitivity. And the uncertainties in aerosol-cloud interactions are the main reason for the largest uncertainty in estimating anthropogenic radiative forcing.

 

    For further readings, you may download the IPCC FAQ document from here.

 

 

FAQ 7.2 | How Do Aerosols Affect Climate and Climate Change? 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     Aerosols are defined as any solid or liquid particles suspended in the air,

with a typical size between a few nanometers (10^-9 meter) to about 10

micrometers (10^-6 meter). They are a mixture of inorganic and organic

substances. In IPCC assessments (since the 2nd one), aerosols are separated

into seven components in models – namely sulfate, black carbon (BC) from fossil

fuel and biofuel, organic aerosol (OA) from fossil fuel and biofuel, BC an OA combined from biomass burning (BB), nitrate, secondary organic aerosol (SOA) and mineral dust (or sea salt). Their lifetimes in the atmosphere can span from one day to two weeks in troposphere, to about one year in stratosphere.

 

     Aerosols can affect climate through their radiative effects on the Earth’s radiation budget. First, they can directly affect the radiation budget by scattering and absorption of solar or Earth radiations. Second, through aerosol-cloud interactions, they can alter cloud cover, thickness, lifetime and thus affecting the climate via cloud radiation effects. Thirdly, they can react with some chemicals (e.g. greenhouse gases) in the atmosphere and therefore, affect their radiative affects. Last but not least, though great uncertainties exist, aerosol have climate feedbacks.

 

     For further readings, you may download the IPCC FAQ document from here.

 

 

FAQ 7.3 | Could Geoengineering Counteract Climate Change and What Side Effects Might Occur? 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

       Geoengineering encompasses two major categories of approaches - the Solar Radiation Management (SRM) and the Carbon Dioxide Removal (CDR) (see figure above).

 

        It has been shown that implementation of SRM can counteract global warming by slowing down the increase of surface mean temperature, possibly at the expense of slight reduction in precipitation rates. However, once the SRM is terminated, the climate system will soon follow the trend as if there were no SRM implementation. In cases of abrupt termination, the temperature / precipitation bounce can be so drastic that great side effect, such as greatly stressing the climate and ecosystems are expected.

 

      For further readings, you may download the IPCC FAQ document from here.