Methane and black carbon cuts won’t buy us time

The warming effect of soot has been exaggerated. Photo: © Buriy - Fotolia.com

Two new scientific studies say that the effectiveness of cutting a range of non-CO₂ gases such as methane and black carbon to limit global warming to 2°C has been strongly and consistently overestimated.

The Guardian reports that the global warming effect of black carbon, or soot, has been greatly exaggerated due to mistaken assumptions about the atmospheric altitude at which its particles are concentrated, according to a study by Norwegian resarchers. “Uncertainty surrounds the exact influence of black carbon on global warming, partly because of the difficulties involved in estimating how much of it is there is. Soot particles are also enigmatic substances, with warming and cooling properties that depend on the atmospheric conditions they encounter as they drift upwards. In the upper troposphere at tropical and middle latitudes, they have the potential to absorb and emit heat and solar radiation. But if they do not rise that far, they may stabilise lower-lying clouds that block the sunlight, so reducing temperatures. Global warming efforts should focus on CO₂, not soot particles known as black carbon”, says the Norwegian team.

The New Scientist reports on a new study published by the International Institute for Applied Systems Analysis, which states that to prevent dangerous climate change, there is no alternative to ending human emissions of carbon dioxide. The study says that “suggestions that cutting a range of non-CO₂ gases like methane might do at least part of the job are based on faulty accounting.” Some scientists and governments have in the past argued that there is a third way to curb warming. Action to reduce other types of greenhouse gas emissions might be cheaper and quicker, buying time for later action on CO₂. The US government and the UN Environment Programme have both promoted cutting emissions of methane and soot as an effective emergency response to global warming. The study says “that the potential for preventing 2°C of warming by controlling these pollutants has been strongly and consistently overestimated.”

The authors of the study explain according to the New Scientist that “the problem is twofold. Because gases like methane have much shorter atmospheric lifetimes than CO₂ they don’t accumulate in the atmosphere in the same way, lessening their contribution to warming. Secondly, these other gases often have the same sources as CO₂ emissions, such as burning fossil fuels. This means that the impact of cutting these gases on curbing climate change has already been included in calculations of cutting CO₂ emissions, so those gases have in effect been ‘double-counted’. Many studies haven’t considered this.”

Reinhold Pape

Sources:
New Scientist, 5 November 2014 by Fred Pearce, Journal reference: PNAS, DOI: 10.1073/pnas.1415631111
Disentangling the effects of CO2 and short-lived climate forcer mitigation. By Rogelj J, Schaeffer M, Meinshausen M, Shindell D, Hare W, Klimont Z, Velders G, Amann M, Schellnhuber HJ. Proceedings of the National Academy of Sciences (PNAS). Link:

Arthur Neslen, Guardian, 26 September 2014
How shorter black carbon lifetime alters its climate effect. By Hodnebrog O, Myhre G, Samset BH. Nature Communications 5.

In this issue

Low in ambition, late in timing

The NRMM proposal presented by the EU Commission shows a lack of ambition in both levels and timing.

Editorial: Ammonia emissions are cheap to reduce

A little more than a century ago Fritz Haber invented a way to make synthetic ammonia out of pure air. The process was soon scaled up for industrial use by Carl Bosch. The method known as the Haber-Bosch process revolutionised agriculture.

Air pollution cuts India’s crop yields by almost half

Ground-level ozone is damaging plants’ leaves and black carbon is reducing the amount of sunlight they receive. Both pollutants are also damaging human health.

UN warns against exceeding “Emissions Budget”

The gap between what countires have pledged to achieve and what the IPCC has estimated is needed in order to stay within the 2°C target is estimated at 10 GT of CO₂e by 2020.

Wind energy – so much potential

We are on track to phase-out and replace fossil fuels with renewable energy. After years of slow growth the wind is now shifting and investment is growing.

Methane and black carbon cuts won’t buy us time

Many loopholes in testing system

European carmakers manipulate emissions testing, so cars on average show 38 per cent lower emissions than under actual driving conditions.

IPCC warns that delaying action implies higher costs

Two-thirds of the carbon budget needed to keep global temperature rise below 2°C has already been spent. To replace fossil fuels we will need to triple our use of zero- and low-carbon energy by 2025.

China: 670,000 smog-related deaths a year

Around 157 million people in China lived in areas where the annual PM_2.5 concentration in 2012 was higher than 100 μg/m³ – ten times the safety limit set by WHO.

Ocean acidification record-high

The rate of ocean acidification is the highest in millions of years. A CBD synthesis and new research show a grim picture in which organisms on the sea floor are particularly at risk.

Biogas from manure

Making biogas from manure results in reduced greenhouse gas emissions and the production of a renewable fuel. The technology is far from its full potential in Europe, but also has some serious limitations.

Air quality targets much cheaper than expected

The EU’s new climate and energy policy for 2030 opens the way for more ambitious clean air targets. The air pollution limits for 2030 proposed by the Commission last December could be achieved at €5.5bn less cost per year when the climate and energy package for 2030 ..

Action needed to cut emissions from domestic solid-fuel burning

Air pollutant emissions from residential heating with solid fuels (wood and coal) are estimated to cause 61,000 annual premature deaths in Europe.

Leave fossil gas in the ground

Gas is better than coal, but not good enough. Much of it has to be left in the ground, so its use has to be cut fast. This is actually happening in Europe. Gas use fell by 13 per cent between 2010 and 2013.

PM pollution requires EU-wide action

Particle pollution is not a purely local problem. Transboundary pollution transport is a major contributor to urban PM_2.5 levels, and reductions in both primary PM and secondary precursor emissions are needed to bring down PM_2.5 to safe levels.

447,000 premature deaths/year in EU due to bad air quality

Elevated levels of air pollutants, primarily fine particulate matter and ground-level ozone, are the top environmental cause of premature death in Europe.

Main menu

Methane and black carbon cuts won’t buy us time

In this issue

Low in ambition, late in timing

Editorial: Ammonia emissions are cheap to reduce

Air pollution cuts India’s crop yields by almost half

UN warns against exceeding “Emissions Budget”

Wind energy – so much potential

Methane and black carbon cuts won’t buy us time

Many loopholes in testing system

IPCC warns that delaying action implies higher costs

China: 670,000 smog-related deaths a year

Ocean acidification record-high

Biogas from manure

Air quality targets much cheaper than expected

Action needed to cut emissions from domestic solid-fuel burning

Leave fossil gas in the ground

PM pollution requires EU-wide action

447,000 premature deaths/year in EU due to bad air quality

Publications

Food for Thought

Northern forests, climate change and the UNFCCC

EU climate targets aligned with the Paris agreement’s 1.5°C objective

Baltic Sea Offshore Wind Collaborative-Learning project

Air pollution in Europe and children’s health

Climate Change: A Himalayan Odessey

No further discussion needed. The agreed global goal is to limit temperature rise to 1.5°C

Fossil-free electricity 2021

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