Can Global Warming be Limited to a Maximum of 2oC ?

One of the great scientific myths of this century is that there exists a large number of “magical” solutions to the climate problem that would limit global warming to less than 2oC using technologies that are currently available and economically feasible if only the political will existed to implement those technologies on a massive scale.  Within the last six months, the scientific and engineering community has begun to openly express doubts as to the feasibility of virtually all of these “magical” solutions. [In fairness, many people within the scientific and engineering communities have long harbored doubts concerning the feasibility of the 2oC objective but have hesitated , for a variety of reasons, to openly express those doubts .]

Magical solutions to the climate/energy crisis fall into two general categories.

The first category of magical solutions is generally referred to as the “100% Renewables by 2050” category, or sometimes as the “Wind, Water and Solar” (WWS) category.   Climate solutions in this category completely phase out fossil fuel use for all purposes (electrical power, transportation, heating/cooling,etc) by mid-century and replace them with wind, water, and solar.  Most solutions in this category also completely eliminate the use of nuclear power.  They all envision historically unprecedented improvements in energy efficiency in housing, commerce and industry.

The second category of magical solutions involves emission pathways which permit the 2oC carbon budget to be exceeded in the first half of this century and then, during the second half of the century, rely on the rapid deployment of so-called “Negative Emissions Technologies” or NETs to remove the excess C02 from the atmosphere.

One of the first to publically and unequivocally state that the 2oC objective is unobtainable was Oliver Geden, who is head of the EU Research Division at the German Institute for International and Security Affairs.  In a paper published in the journal Nature in May of this year he writes,

“The climate policy mantra – that time is running out for 2oC but we can still make it if we act now – is scientific nonsense.  Advisors who shy away from saying so squander their scientific reputations and public trust in climate research”.

He goes on to state,

“Scientific advisers should resist the temptation to be political entrepreneurs, peddling their advice by exaggerating how easy it is to transform the economy or deploy renewable technologies, for instance.”

Another outspoken advocate for a more realistic assessment of climate change mitigation is Kevin Anderson, deputy director of the Tyndall Centre, the UK’s leading academic climate change research organization.  In a paper published in the December 2015 issue of Nature Geoscience, he states,

“Delivery of palatable 2oC mitigation scenarios depends on speculative emissions or changing the past.  Scientists must make their assumptions transparent and defensible, however politically uncomfortable the conclusions”.

It has been known since 2009, based on a series of landmark analyses published in that year, that the cumulative emissions of CO2 over time will largely determine the level of global warming that will occur during this century and beyond.  The IPCC’S Synthesis Report issued last year concludes that no more than 1,000 billion metric tons of CO2 (1,000 GT) can be emitted between 2011 and 2100 for a 66% chance, or better, of remaining below a 2oC rise in global mean temperature.  Between 2011 and mid-2015 approximately 150 GT of CO2 was emitted into the atmosphere.  At the current global CO2 emissions rate, the remaining 850 Gt will be emitted well before 2040.  Even assuming that the emission pledges made by some 140 nations in the lead-up to the Paris Climate Conference are fully met, the 2oC carbon budget will be exceeded well before mid-century.

So why the optimism in the lead-up to the Paris Conference?  In large measure it is based on the assumption that even if we exceed the2oC emissions budget during the  first half of the century we can make up for it  during the second half of the  century through the magical powers of “negative emissions”.  The basic concept is referred to as bioenergy with carbon capture and sequestration, or BECCS.  The idea is to harvest trees or other crops which remove carbon from the atmosphere, burn them to create electricity, capture the CO2 emitted and bury it deep underground.  There are numerous problems with the BECCS concept, not the least of which is the immense amount of land required to have any real effect on global climate.

A recent study published in the journal Nature Climate Change provides a detailed and realistic assessment of negative emissions technologies (NETs), including BECCS.  It demonstrated that emissions scenarios which are consistent with a 2oC target require approximately 3.3 Gt of carbon (which is equivalent to 12.9 billion tons of CO2) to be removed from the atmosphere each year by 2100.  To achieve this level of negative emissions would require an amount of land roughly the size the entire continental US!  The study reached the following conclusions,

“…a heavy reliance on negative emission technologies (NETs) in the future, if used as a means to allow continued use of fossil fuels in the present, is extremely risky…. A failure of NETs to deliver expected mitigation in the future, due to any combination of biophysical and economic limits examined here, leaves us with no ‘Plan B’.  As this study shows, there is no NET (or combination of NETs) currently available that could be implemented to meet the <2oC target without significant impact on either land, energy, water, nutrient, albedo or cost, so ‘Plan A’ must be to immediately and aggressively reduce GHG emissions.”

Slowly, it is becoming apparent to the scientific and engineering communities that it is no longer rational to cling to a climate objective that quite simply can not be achieved without reliance on “magical” solutions.  And YES this means that humanity will face climatic conditions that it has never experienced throughout its entire evolution.

There can be no doubt that the world needs to immediately and aggressively reduce GHG emissions, even though it will unavoidably cross the 2oC threshold well before mid-century.  To continue to pretend that there exists a “magical” solution to the climate change problem lends credence to the all too widely held belief that the climate change problem is less dire then it truly is, and will inevitably delay the radical changes required in the global economy if we are to avoid crossing the 3oC threshold!