No 1971 Posted by fw, June 3, 2017
“…if we wish to stay below 2 degrees C of warming, we have a fixed budget of CO2 emissions that we can emit between now and 2050. Reducing emissions slightly won’t solve the problem as global warming won’t stop getting worse until we reduce CO2 emissions to a rate which is less than CO2 is being removed from the atmosphere. The longer we wait before the world peaks its emissions, then the faster we need to cut emissions after that peak in order to stay within our cumulative emissions budget…. ‘Political reality must be grounded in physical reality or it’s completely useless’” —Dr. Aaron Thierry, University of Sheffield
Dr. Thierry received his PhD in Ecology from the University of Sheffield: he subsequently researched the impacts of global warming on the carbon cycle in Arctic ecosystems.
The following post is excerpted from Dr. Thierry’s May 2014 paper: The climate crisis: a period of consequences.
At the bottom of this post is an embedded 77-minute video of Dr. Thierry’s talk on climate change delivered this year at the University of Sheffield.
The cumulative level of CO2 in the atmosphere will continue to rise if we don’t reduce our fossil fuel use
Many people feel that we have plenty of time to reduce carbon emissions and that the threat is a long way off – they could not be more wrong. The most important point here is to appreciate that we are dealing with a stocks and flow problem. The best analogy is that of a bathtub. Imagine we are filling a bath. What matters to the level of the bathwater is the difference between the rate water flows in and the rate it flows out. So long as the inflow exceeds the outflow the bath will overflow – we will have exceeded our target!
It’s the cumulative emissions that determine the planet’s temperature, not the rate at which we are emitting CO2
Now the atmosphere is that bathtub into which we are pouring CO2 far faster than it leaves (a molecule of CO2 typically stays in the atmosphere for 100 years or more), as such the cumulative emissions are amassing, and the concentration in the atmosphere is steadily increasing. This is the crucial point as it is the cumulative emissions that determine the planet’s final temperature, not the rate at which we are emitting greenhouse gases at any given date in the future.
To stay below 2°C, we must not exceed the fixed budget of CO2 we can emit between now and 2050
Once we grasp this point we realise that, if we wish to stay below 2°C of warming, we have a fixed budget of CO2 emissions that we can emit between now and 2050. Reducing emissions slightly won’t solve the problem as global warming won’t stop getting worse until we reduce CO2 emissions to a rate which is less than CO2 is being removed from the atmosphere.
The longer we wait before the world peaks the level of its cumulative emissions, the less time we will have to cut our emissions
The longer we wait before the world peaks its emissions, then the faster we need to cut emissions after that peak in order to stay within our cumulative emissions budget.
The diagram in Figure 12 illustrates the point, bear in mind that it is the area under each curve that matters:
Figure 12. Three scenarios with a cumulative emissions budget for a 67% chance of staying below 2°C. The different coloured lines represent different peak emissions dates, green is 2011, blue is 2015, red is 2020. The longer we wait before reducing emissions the faster we must then reduce emissions in order to remain within the same emissions budget. The area under each curve is the same i.e. the same total amount of carbon has been emitted. [Source: The Copenhagen Diagnosis, 2009: Updating the World on the Latest Climate Science, The University of New South Wales. Climate Research Centre, Sydney, Australia, 60pp.]
We can no longer think in terms of long-term targets; instead we must aim to peak and then reduce emissions as soon and as fast as we can
This completely changes how we must approach this problem as we can no longer think in terms of long‐term targets, we must instead urgently aim to peak and then reduce emissions, as the longer we wait the harder and more costly the change will be.
Scientific outcomes are always stated as probabilities – the higher the probability of staying below 2°C, the lower the amount of carbon we can burn
What I haven’t mentioned yet is that because of uncertainties in our understanding, the science can only offer probabilistic carbon budgets. We can make a statement such as this; to have an 80% chance of staying below 2 degrees we can only afford to emit 886 Gigatonnes of carbon between 2000 and 2050 (we’ve already burnt through 321 Gigatonnes). It strikes me as important to point out that an 80% chance is worse odds than playing Russian Roulette with a six shooter! Of course, if we’re prepared to accept worse odds still then this budget gets bigger. A 1,440 Gigatonne budget between 2000‐2050 would give a coin flip’s (50:50) chance of staying under 2°C [Source: Greenhouse-gas emission targets for limiting global warming to 2°C by Malte Meinshausen et al., Nature, April 30, 2009]. The U.K. Government has currently adopted a much larger carbon budget that only gives us only a 37% chance of staying below 2 degrees! [Source: Real clothes for the Emperor, by Kevin Anderson, kevinanderson.info, March 2013].
Politicians will resist adopting an urgent and radical approach to dealing with climate change
The importance of the concepts of carbon budgets cannot be overstated. It shows us that we must adopt an urgent and radical approach to dealing with Climate Change, we cannot delay action any further. It also makes plain that the idea of long‐term reduction targets is shown to be scientifically meaningless, but they are comfortably outside of current politicians’ time in office.
To stay below 2°C, the UK would have no choice but to make swift and large cuts in energy demand; renewables could not be scaled up fast enough to help
One recent and credible estimate from members of the Tyndall centre suggests that to do its equitable share for a 63% chance of staying under 2°C, the U.K. must begin cutting emissions at a rate of almost 8‐10% per annum. That is a 40% reduction on 1990 emission levels by 2015, a reduction of 70% by 2020‐2025 and 95% reduction by 2030‐2035. The implication of the need for such swift reductions in fossil fuel use is that they can only be achieved (in the short term at least) by reductions on the energy demand side, as there simply is not enough time to build replacement green energy supplies.
Moreover, demand cuts will require large-scale social and behavioural changes
Demand side reductions will require large-scale social and behavioural changes as well as the adoption of highly efficient end use technologies.
HERE’S THE KICKER – We already have far more fossil fuels in reserve than we can safely burn
One other crucial fact follows from the concept of a carbon budget and that is that we can compare the size of the budget to the size of our known fossil fuel reserves. If we do this then we find that, if we want an 80% chance of staying below 2 degrees C, we have five times the necessary fossil fuel reserves [Source: The Most Influential Climate Science Paper Today Remains Unknown to Most People by Katherine Bagley, Inside Climate News, February 14, 2013].
Even the IEA admit that for only a 50% chance we would still need to leave two thirds of our available fossil fuel reserves in the ground, unburned! [Source: IEA acknowledges fossil fuel reserves climate crunch by Lorne Stockman, Oil Change International, November 12, 2012].
It is according to the logic of this argument that we can easily claim that it is entirely incongruent for our Government to be thinking of allowing the development of shale gas in the U.K. as the World already has far more fossil fuels then it can safely use.
“The 2°C target is largely out the window”
The scale of this challenge is enormous, and has led many leading policy experts and climate scientists to declare that this target is impossible in the current political context. Prof. Sir Bob Watson, former co-chair of the IPCC and chief scientist to DEFRA, recently stated his opinion that the “2°C target is largely out of the window.” [Source: Science adviser warns climate target ‘out the window’ by Pallab Ghosh, BBC News, August 23, 2012].
Can we say living with the consequences of a 4°C warmer world is any more possible?
However, we have to really consider the alternative scenario here; can we in any meaningful sense say that living with the consequences of a 4°C warmer world is any less impossible?
“Political reality must be grounded in physical reality or it’s completely useless”
Prof. Hans Schellnhuber, director of the Potsdam institute and an advisor to the German Chancellor once pointed out that “Political reality must be grounded in physical reality or it’s completely useless”. [Source: CLIMATE CHANGE: Four Degrees of Devastation, by Stephen Leahy, Inter Press Service, October 9, 2009]
Clearly, business-as-usual is not an option
Quoting a new Pricewaterhouse Coopers report “Too late for two degrees?” on the matter we can say confidently that “business‐as‐usual is not an option” [Source: PwC Low Carbon Economy Index 2012: Too late for two degrees? by Price Waterhouse Coopers].
Aaron Thierry: The Brutal Logic of Climate Change (March 2017) Published on May 24, 2017 — Full length 87-minute talk that covers the facts of climate change, the urgency with which it needs to be addressed and actions we can take to stop it. Delivered by Dr Aaron Thierry at the University of Sheffield, hosted by the Carbon Neutral University Network.
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