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Could we control our climate?
Could we control our climate?

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3.2 Our current path

Could we meet the Paris Agreement targets (well below 2 °C above preindustrial climate, pursuing efforts for 1.5 °C) just by reducing greenhouse gas emissions and no geoengineering?

The first question is: where are we heading? Current global emissions are close to, or slightly higher than, the RCP8.5 scenario (Figure 6).

Figure 6 is a line graph of global emissions of carbon dioxide in picograms per year on the y or vertical axis (from -1 to +29) against year (from 1980 to 2100) on the x or horizontal axis. Five lines are shown. The first line plots observed emissions and increases from about 5 to 10 picograms per year in 1980 to about 11 picograms per year in 2014. This end point lies just above the RCP8.5 scenario. Four lines are used to show forecast data for emissions from 4 RCP multi-model scenarios, from about 2010 with emissions of about 9 picograms per year : Yellow RCP2.6 – steady decrease of emissions to about -1 picograms per year by 2100 , labelled with a temperature rise of 1.5 °C by 2100 (relative to preindustrial levels) Green RCP4.5 – steady increase of emissions until about 2040 then a decrease to about 4 picograms per year by 2100, temperature rise of 2.4 °C by 2100 Blue RCP6.0 – steady increase of emissions until about 2080 then a decrease to about 14 picograms per year by 2100 , temperature rise of 3.0 °C by 2100 Orange RCP8.5 – steady increase of emissions to about 29 picograms per year by 2100 , temperature rise of 4.9 °C by 2100
Figure 6 Emissions of CO2, observed (black dots) and for the RCP scenarios (coloured lines) (Sanford et al., 2014). Numbers on the right-hand side are the median and 66% probability range of GMST projections above preindustrial levels in 2100 by Rogelj et al. (2012).

If we continue on this very high pathway, our odds of exceeding 4 °C warming this century are about 50–50. In other words, as far from preindustrial climate as the last ice age was in the opposite direction. However, following RCP8.5 would require rapidly increasing emissions and it can be considered a ‘no climate policy’ (or worse) scenario – something that we do not have.

How far would current policies and pledges take us?

The website climateactiontracker.org tracks the effects of policies and pledges on our future climate. Perhaps unsurprisingly, predicted temperatures for pledges are higher than the targets, and those for current policies are higher still.

  • Visit climateactiontracker.org [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] ‘Global’ page. Have these predictions changed at all ?

  • In December 2019, the predicted temperature under current pledges had actually increased by 0.1 °C, to 2.8 °C, while the lower bound for current policies had decreased by the same amount. The answer for future years is unknown, though both are intended to decrease with time.

Pledges are based on current knowledge: unpredictable aspects – such as technology, energy use and political will – will affect the ability of nations to reduce their emissions. To respond to this the Paris Agreement outlines an iterative approach of re-evaluating and repledging every five years, this is known as a ‘ratchet’ mechanism.