So I’ve been wrapping my head around possible ways to achieve the goal of keeping average global temperatures within 2°C of the 2000 level for remainder of 21st century. A huge expansion of carbon capture and storage (CCS) technology would help – but how feasible is it? Currently, not very.

Summary so far: to keep average global temperatures within 2°C by 2100, we’ll need to be a lot more energy efficient, reproduce less (not exceeding 9 billion by century’s end), and get really good at increasing agricultural productivity so that lots of land can revert back to the wilds. Scenarios associated with RCP2.6 show how this might be possible.

RCP2.6 is one of the four Representative Concentration Pathways (RCPs) presented by the Intergovernmental Panel on Climate Change (IPCC) a few years ago. A scenario consistent with RCP2 is a global population of 9 billion in 2100, fairly robust global GDP growth, middling reforestation and wild habitat restoration,  relatively less oil (and more natural gas) consumption than the other RCPs, and decent advances in carbon capture technologies van Vuuren et al (2011a).

What to do about climate change? Initiate the Process. The first few steps being: define the Problem, then specify what you want to accomplish (the goal) and what you want to avoid.

The basic message of the last few posts: climate change projections require assumptions about human behavior and these assumptions may be questionable. For instance, the Intergovernmental Panel on Climate Change (IPCC) has presented a “business-as-usual” trajectory of green house gas concentrations that would result in a mean global temperature rise of 3.7°C (2.6 to 4.8°C range) by 2100, meaning that such concentrations are plausible if present trends continue.

“Coal is the slowest-growing energy source in the IEO2016 Reference case, with 0.6%/year average increases in total world coal consumption from 2012 to 2040, considerably slower than the 2.2%/year average over the past 30 years. The EIA forecasts declines from 40% of total generation in 2012 to 29% in 2040.” (IEA)

In terms of predicting climate change and its effects, it’s essential to get population projections right.  And in terms of climate change mitigation, the fewer humans the better. Per O’Neill et al, every 1% decrease in global population would mean a 1% decrease in emissions.

According to the scientists who proposed RCP8.5 [the scariest projection of atmospheric GHG concentrations], its trajectory is plausible based on assumptions of “…low income, high population and high energy demand due to only modest improvements in energy intensity.”   Are these assumptions reasonable based on current trends - that is, do they represent a plausible“business-as-usual” scenario? Let's look at income first.

Representative Concentration Pathways (RCPs) represent possible trajectories of atmospheric concentrations of green house gases (GHGs) over the next century.  The RCPs are named after their targeted heating effects. For instance, RCP8.5 represents a trajectory that could result in atmospheric heating of 8.5 watts per meter squared by 2100. RCP8.5 is the most extreme of the four RCPs considered by the IPCC.  It projects a mean temperature rise of 3.7°C and a likely increase range of 2.6 to 4.8°C by 2100, wreaking all sorts of havoc along the way.

The Intergovernmental Panel on Climate Change (IPCC) has laid out a range of scenarios for what might happen to the planet, atmosphere, biosphere, and human society over the course of the next century. These scenarios are based on different “Representative Concentration Pathways” (RCPs), each with its own story line about population growth, economic activity, land use patterns, energy use, lifestyle, climate policy, and mitigation efforts. 

Just 10% of Americans currently say that human-caused climate change is not happening or is not about to happen. Climate change “dismissives” are a vanishing species. Disagreement is mostly about how fast, how much, possible effects and what the best course of action is.

Sometimes when I sound a note of hope about climate change, others seem irritated or even angry. As if hope negates strong measures, and unless we take strong measures, the situation is truly hopeless.  As if hope engenders complacency. But hope can spur action, especially hope tempered by a sense of urgency and an understanding that sacrifice is also part of the equation.

My last post ended on a note of optimism: continued economic growth, cultural change and technological development can go a long way in ameliorating climate change, and the effects thereof. In short: with economic development, empowerment of women, intensification of sustainable agriculture, and urbanization, human populations plummet and wild habitat expands. ...

Ignoring possible human suffering and death caused by climate change adaptation and mitigation efforts is no different than drone pilots disassociating from the effects of their bombing runs. Of course, sometimes drastic – and lethal – measures are justified. But trade-offs are involved – and if you care about human life, trade-offs must be seriously considered.

We know that a lot of people will die because of the havoc wreaked by climate change. The (WHO) estimates that between 2030 and 2050, climate change will cause roughly 250 000 additional deaths per year, from malnutrition, malaria, diarrhea and heat stress.

Climate change action priorities, simplified version: reduce green house gases, protect habitats, protect wildlife and protect humans. For this post, I’m going to focus on protecting humans – operationalized as reducing the extra deaths caused by climate change. A huge factor in reducing climate-change related deaths is economic development. Specifically, as GDP increases, mortality rates decrease. Mean death rates fall by 15% for every 10% increase in GDP. And we’re not just talking about old people getting a couple extra years: on average, a 10% increase in income means a 5% fall in infant mortality.

"Climate change could kill more than 500,000 adults in 2050 worldwide due to changes in diets and body weight from reduced crop productivity, according to new estimates. The research is the strongest evidence yet that climate change could have damaging consequences for food production and health worldwide." - Springmann et al (2016)