Yesterday I expressed some frustration with the fact that the IPCC’s attempt to summarise its latest report on the potential impacts of climate change lacked clear guidance on the what we’re in for if we don’t act to curtail carbon emissions.
Then I read one scientist’s quote which seemed to so sharply cut through the 30 chapters and hundreds and hundreds of pages of the report to give us the very essence of what’s important. Dr Rachel Warren, from the UK’s Tyndall Centre and a co-ordinating lead author on the Emergent Risks and Key Vulnerabilities chapter of the IPCC’s impacts assessment, said:
“There’s a lot we can’t adapt to even at 2 C [degrees}. At 4 C [degrees] the impacts are very high and we cannot adapt to them. Reducing emissions reduces global temperature rise, and also the rate of temperature rise. This makes it easier to the adapt to the remaining impacts. We’ve left it too late to reduce emissions enough to avoid all of the impacts of climate change, but we could still avoid a large proportion of them by reducing emissions soon, and fast.”
To better appreciate her point you need to delve into Chapter 19, and in particular section 19.5. This details the kind of impacts we are likely to see with 4 degrees of warming. As pointed out yesterday, forecasts by the International Energy Agency suggest that on the basis of current government policies, emissions are likely to reach a level where we have an even-money chance of exceeding 4 degrees (above pre-industrial levels) by the end of the century.
To take one important example, in agriculture the effects of global warming aren’t all bad in the short-term and with moderate warming. While we would probably see losses in agricultural yields in tropical and mid-latitudes even with just 2 degrees of warming (see this article – Countdown to a crop yield cut – for a rundown on the latest research), there would be compensating improvements in yields at higher northern latitudes. But to underline the severity of a 4-degree rise the IPCC notes that even for Finland this would lead to a reversal of earlier gains in agricultural yield and ultimately “substantial reductions”.
Also, rainfall effects would be devastating in some regions with the report noting that annual runoff is projected to fall by up to 75 per cent across the Danube, Mississippi, Amazon and Murray Darling river basins.
Also, Chapter 7 notes:
Under scenarios of high levels of warming, leading to local mean temperature increases of 3-4 degrees or higher, models based on current agricultural systems suggest large negative impacts on agricultural productivity and substantial risks to global food production and security (medium confidence).
Furthermore, emerging research has found that while increased levels of CO2 will enhance growth, it could lead to reductions in the nutritional value of crops. Chapter 19 notes:
A prominent example of the effect of elevated atmospheric CO2 is the decrease in the nitrogen (N) concentration in vegetative plant parts as well as in seeds and grains and, related to this, the decrease in the protein concentrations. Experimental studies of increasing CO2 to 550 ppm demonstrated effects on crude protein, starch, total and soluble Β-amylase, and single kernel hardiness, leading to a reduction in crude protein by 4 to 13% in wheat and 11 to 13% in barley. Other CO2 enrichment studies have shown changes in the composition of other macro- and micronutrients (Ca, K, Mg, Fe, Zn) and in concentrations of other nutritionally important components such as vitamins and sugars
Another example it cites of the limits to adaptations from a 4-degree world is just sheer heat stress:
Under 4-degree warming most of the world land area will be experiencing 4 to 7-degree higher temperatures than the recent past which means that important tipping points for health impacts may be exceeded in many areas of the world during this century, including coping mechanisms for daily temperature/humidity making potentially large areas seasonally uninhabitable for normal human activities, including growing food or working outdoors (high confidence).
Is it too late?
Chapter 19 of the report notes that there are very few analyses that have demonstrated we could feasibly contain warming to 1.5 degrees with a 50 per cent chance or better. However, a number of studies have shown that it is still technically feasible to achieve a 50 per cent of chance or better of keeping temperature rise to 2 degrees. But they note that these studies include:
...a number of idealised assumptions, including availability of a wide range of mitigation technologies such as large-scale renewable and biomass energy, and carbon capture and storage (CCS). Most also assume universal participation in mitigation efforts beginning immediately, economically optimal reductions (i.e., reductions are made wherever they are cheapest), and no constraints on policy implementation.
It looks like we better prepare ourselves to adapt to at least a 2-degree warmer world. But we really don’t want to be forcing our children and grandchildren to have to adapt to a 4-degree warmer planet.