Future climate change, climate impacts, climate change adaptation and emissions mitigation can be viewed from different perspectives, each with their own characteristics. Here we look at three main perspectives, or different ‘lenses’ that can be used. These are also called ‘dimensions of integration’.
Showing change through time or at various periods under different plausible future emissions pathways, derived by considering a range of socio-economic and technological scenarios. This is the most widely used and understood method – and is the lens used for most climate projections information on the Climate Change in Australia website.
Why use this?
This method gives a view of change through time, including different potential paths that diverge as they go further into the future. The method makes it easy to relate climate changes to different planning time frames and to relate different amounts of greenhouse gas emissions (the emissions pathways) to the projected climate change and associated impacts.
An alternative to looking through the lens of emissions pathways is to look at global warming: the change in the climate when the Global Mean Surface Temperature (GMST) is consistently at a temperature ‘level’ warmer than a pre-industrial climate, say +2 °C
A suitable baseline before the industrial era began would be 1720–1800, but climate observations are poor in this period. A period that is a balance between data availability and low industrial activity of 1850–1900 has been widely accepted, including for the Intergovernmental Panel on Climate Changes (IPCC) assessments, as a proxy for the preindustrial cliamte (for more detail see). We don’t have a precise estimate of the amount of warming for a given increase in greenhouse gas concentration (known as ‘climate sensitivity’), so for any emissions pathway there is a range of possible dates when a level could be reached (and models give different results).
Climate change and impacts within a region (a continent, a country or area within a country) can be related to the level of global warming from this 1850-1900 baseline and can be quantified for different warming levels.
Why use this?
A major practical reason to use this lens is that the Paris Agreement (2015) is framed around global warming levels, with the goal to keep global warming well below +2 °C and to aim for less than +1.5 °C. Consequently, many discussions and analyses use this frame of reference. For example, the Taskforce on Climate-related Financial Disclosures (TCFD) international guidelines now recommend using this lens.
But what is the deeper reason for this framing, and why did the Paris Agreement use it? Changes to Global Mean Surface Temperature (GMST) can be roughly related to the scale of climate impacts experienced. A popular way to visualise the increasing risks with rising global average temperature is the ‘reasons for concern’ or ‘burning embers’ diagram.
For more on the global changes and impacts at the 1.5 and 2 °C warming levels, see(new window).
For more on the ‘burning embers’ diagram and changes to it through time, see(new window).
A third lens through which we can view the future climate is the cumulative total anthropogenic carbon dioxide emissions – the total emissions humans have emitted over time since the pre-industrial baseline climate (often quantified as emissions since 1870). This starts with the global warming level lens, and then goes on to relate this global warming to cumulative CO2 emissions as the most abundant anthropogenic greenhouse gas. In the past and for the rest of this century, our total carbon emissions are directly related to Global Mean Surface Temperature increase, in an almost straight-line relationship. Therefore, regional temperature change, climate impacts, and adaptation decisions can be roughly related to cumulative global carbon emissions and the global emissions reduction that this involves.
The near linear relationship between cumulative CO2 emissions and the global temperature change can be visualised in this schematic adapted from:and , see these sources for more information (new window)
Why use this?
This method allows the analysis of climate change and its impacts in the context of carbon and emissions ‘budgets’ – to directly relate climate impacts to mitigation efforts and policies at a global scale. This is useful for global discussions of emissions mitigation policy and strategy.