greenhouse gas emissions and the intergovernmental panel on climate change (IPCC) reports

main objective of IPCC

supply world with a clear scientific view on the current state of knowledge in climate change and its potential environment and socio-economic impacts

first assessment report (FAR) 1990

International attention drawn to problem of climate change

second assessment report 1995

A key input document to the adoption of the Kyoto protocol in 1997

AR6 climate change 2021

• Observations of the climate system

• Paleoclimate archives

• Theoretical studies of climate processes

• Simulations using climate models

It builds upon the working group I contribution to the IPCC's AR5

AR5 possible future scenarios

Representative concentration pathways are climate change scenarios use to project future greenhouse gas concentrations

radiative forcing

a direct measure of the amount that the earth's energy budget is out of balance

RCPs

effectively calculate the concentrations of greenhouse gases that is likely to produce an increase in total radiative forcing to some target value in the year 2100, compared with the pre-industrial period

TOA

Total radiative forcing is incoming minus outgoing solar radiation at the top of the atmosphere

5 qualitative descriptions of future changes in demographics

human development, economy and lifestyle, policies and institutions, technology and environment and natural resources

climate models

Very complex computer programmes which describe the most important components, processes and interactions in the climate system

grid boxes

For each grid box, the model calculates how these parameters change from one point in

time to the next, and how this affects neighbouring boxes. The amount of data that has to be processed is immense: the model has to calculate a range of physical parameters for millions of grid boxes and repeat the process innumerable times

GCMs

general circulation models

GCMs description

complex atmosphere/ocean models which can be coupled to models of vegetation, ice etc. They are used for IPCC overall forecasts.

Idealised models are simple models which can be used to explore specific mechanisms

sinks

Fossil fuel burning overtook land use change as the main driver of CO2 emission in the mid-20th century. The ocean has taken up ~29% of total CO2 emissions over the last decade, with ~50% going into the atmosphere.

how long will extra CO2 remain in the atmosphere

CO2 is chemical stable in the atmosphere (unlike methane). CO2 does not have a specific lifetime because it is continuously cycled between the atmosphere, oceans and land biosphere. About 30% of the anthropogenic CO2 will be removed over a time scale of 30 years. A further 30% will be removed over a few centuries. Remaining 40% will remain in this atmosphere for several thousand years.

climate sensitivity

The equilibrium climate sensitivity is a measure of the climate system response to sustained radiative forcing.

It is defined as the equilibrium global average surface warming following a doubling of CO2 concentration with respect to pre-industrial levels.

ECS of 3 degree C meaning

If atmospheric CO2 increases from 280ppm to 560ppm, average global surface temperatures will be 3°C warmer than pre-industrial levels. However, some parts of the globe will almost certainly warm much more than this.

Climate feedback processes (e.g. effect of clouds) are known to play a critical role in uncertainties in climate sensitivity within climate model

uncertainties

• Climate-carbon feedbacks

• The cloud albedo effect

• Effect of stratospheric water vapour

• Effect of solar forcing

• Ice sheet behaviour

• Effect of linear contrails from aircraft

climate system feedbacks

• Tropospheric water vapour changes - positive 

• Sea-ice albedo feedbacks - positive

• Warming reduces terrestrial and ocean CO2 uptake - positive

• Cloud cover - positive and negative