1.5 Celsius Target Likely To Be Exceeded
The Paris 2015 agreement by the United Nations Framework Convention on Climate Change (UNFCCC), at their Conference of Parties (COP) meeting, strives to limit global warming (or anthropogenic climate disruption (ACD)). The aim was to limit warming to 2 °C since pre-industrial times, or possibly even 1.5 °C. The ambitious target would require serious emission reductions on a global scale. Now this Huntingford & Mercado research in Scientific Reports suggests that even if the climate is stabilised at current atmospheric greenhouse gas (GHG) concentrations, then the warming targets are still likely to be exceeded over land. This is mainly for two reasons: firstly current transient warming lags behind “equilibrium or committed warming” and secondly climate models show warming rates over land are much higher than those for the oceans.
The article by Chris Huntingford & Lina M. Mercado was published in July 2016. It highlights the fact that additional warming will likely impact terrestrial ecosystems and human wellbeing. The COP21 (Conference of Parties twenty-first) meeting at Paris highlighted the challenge of hitting the 1.5°C to 2°C targets. The targets would need a year-on-year emissions reduction of at least 2% per annum or more. This reduction would need to start very soon. Already Nature has highlighted that, collectively as a society, we have used two thirds of our allowance of cumulative carbon dioxide (CO2) emissions to keep the temperature below the two degrees target. If we could stop all greenhouse gas (GHG) emissions now then atmospheric temperatures will subsequently reduce very slowly over very long time frames (more than decades). As a result it will become difficult to return from any warming levels we have already committed to.
When there is an increase in carbon dioxide levels there is an initial increase in warming associated with the additional gas concentrations. This initial increase is known as the transient warming. This is not the complete story though as the warming will continue over a much longer time frame which occurs as the carbon dioxide concentration stabilises in the atmosphere. The longer time period is known as the equilibrium or committed warming. Further details of the differences can be read about on this University of Washington link or this Climate Emergency Institute link. It is important to understand the main difference between the transient warming and the equilibrium warming.
Equilibrium climate sensitivity relating GHG concentrations (to any final stable warming levels) remains highly uncertain in all current climate models. Having studied a number of models though, it appears the majority of models suggest that the equilibrium or committed temperature change will exceed the 1.5°C target. In fact it is 17 out of the 22 models that suggest this temperature increase will be exceeded. Ten models suggest that the 2°C target will be exceeded. 16 models show that the global temperature increase will exceed 1.5°C and 10 (out of the 22) exceed 2°C. The land based temperature increases are projected to be significantly higher than for oceans. 17 out of the 22 models show an increase greater than 2°C for the land based warming. As a result the hotter global mean temperature increase will actually have a larger impact on human societies and terrestrial ecosystems.
This article analysed many global climate models (GCM) and explores some committed warming scenarios from these models. The authors show that there is a “very high probability …[of]… a mean warming over land greater than 1.5 °C relative to pre-industrial times”. The rises are likely to impact different areas in different ways. There are likely to be much higher warming rates in the northern latitudes during the boreal winter for example. Away from coastal areas there are likely to be increased warming too. Recent measurements in East Asia back up this figure. It is still very difficult to predict the precise impacts largely to model output differences. Recent data from the US National Oceanic and Atmospheric Administration (NOAA) and others have highlighted 2016 to be another record breaking hot year. The July global land and ocean surface temperature increases have been recorded at 0.87°C above the twentieth century average temperature range.
It is highly likely that Chris Huntingford & Lina M. Mercado are going to be correct in their predictions. The implications for humans on planet Earth should not be underestimated especially with regard to the impacts on agricultural production especially crop viability. The impacts are likely to vary around the globe and there will be severe impacts on hydrological cycles in some areas.