[Note: This item comes from friend David Rosenthal. DLH]
Is the 2 °C world a fantasy?
Countries have pledged to limit global warming to 2 °C, and climate models say that is still possible. But only with heroic — and unlikely — efforts.
By Jeff Tollefson
Nov 24 2015
The year is 2100 and the world looks nothing like it did when global leaders gathered for the historic climate summit in Paris at the end of 2015. Nearly 8.8 billion people now crowd the planet. Energy consumption has nearly doubled, and economic production has increased more than sevenfold. Vast disparities in wealth remain, but governments have achieved one crucial goal: limiting global warming to 2 °C above pre-industrial temperatures.
The United Nations meeting in Paris proved to be a turning point. After forging a climate treaty, governments immediately moved to halt tropical deforestation and to expand forests around the globe. By 2020, plants and soils were stockpiling more than 17 billion tonnes of extra carbon dioxide each year, offsetting 50% of global CO2 emissions. Several million wind turbines were installed, and thousands of nuclear power plants were built. The solar industry ballooned, overtaking coal as a source of energy in the waning years of the twenty-first century.
But it took more than this. Governments had to drive emissions into negative territory — essentially sucking greenhouse gases from the skies — by vastly increasing the use of bioenergy, capturing the CO2 generated and then pumping it underground on truly massive scales. These efforts pulled Earth back from the brink. Atmospheric CO2 concentrations peaked in 2060, below the target of 450 parts per million (p.p.m.) and continue to fall.
That scenario for conquering global warming is one possible — if optimistic — vision of the future. It was developed by modellers at the Joint Global Change Research Institute in College Park, Maryland, as part of a broad effort by climate scientists to chart possible paths for limiting global warming to 2 °C, a target enshrined in the UN climate convention that will produce the Paris treaty.
Climate modellers have developed dozens of rosy 2 °C scenarios over several years, and these fed into the latest assessment by the Intergovernmental Panel on Climate Change (IPCC). The panel seeks to be policy-neutral and has never formally endorsed the 2-degree target, but its official message, delivered in April 2014, was clear: the goal is ambitious but achievable.
This work has fuelled hope among policymakers and environmentalists, and it will provide a foundation for debate as governments negotiate a new climate agreement at the UN’s 2015 Paris Climate Conference starting on 30 November. Despite broad agreement that the emissions-reduction commitments that countries have offered up so far are insufficient, policymakers continue to talk about bending the emissions curve downwards to remain on the path to 2 degrees that was laid out by the IPCC.
But take a closer look, some scientists argue, and the 2 °C scenarios that define that path seem so optimistic and detached from current political realities that they verge on the farcical. Although the caveats and uncertainties are all spelled out in the scientific literature, there is concern that the 2 °C modelling effort has distorted the political debate by obscuring the scale of the challenge. In particular, some researchers have questioned the viability of large-scale bioenergy use with carbon capture and storage (CCS), on which many models now rely as a relatively cheap way to provide substantial negative emissions. The entire exercise has opened up a rift in the scientific community, with some people raising ethical questions about whether scientists are bending to the will of politicians and government funders who want to maintain 2 °C as a viable political target.
“Nobody dares say it’s impossible,” says Oliver Geden, head of the European Union Research Division at the German Institute for International and Security Affairs in Berlin. “Everybody is sort of underwriting the 2-degree cheque, but scientists have to think about the credibility of climate science.”
Modellers are first to acknowledge the limits of their work, and say that the effort is designed to explore options, not predict the future. “We’ll tell you how many nuclear power plants you need, or how much CCS, but we can’t tell you whether society is going to be willing to do that or not,” says Leon Clarke, a senior scientist and modeller at the Joint Global Change Research Institute. “That’s a different question.”