November 2013 – Cabot Institute for the Environment blog

Carbon dioxide is the most important greenhouse gas produced by human activities, and one which is likely to cause significant global climate change if levels continue to increase at the current rates. This year’s Global Carbon Budget holds disappointing yet hardly unexpected news; in 2012, carbon dioxide (CO₂) emissions rose by 2.1% to the highest levels in human history, a total of 9.7 billion tonnes.

CDIAC Data; Le Quiere et al 2013. Global Carbon Project 2013. Data not adjusted for leap year.

The annual Carbon Budget report is compiled by the Global Carbon Project, a collaboration of 77 scientists from around the world including the Cabot Institute’s own Dr Jo House. They predict that in 2013, global carbon emissions will have increased by a further 2.1%, setting a new record high.

Major CO₂ emitters

China produced the most CO₂ in 2012 (27% of total), which was almost twice as much as the second worst offender, the USA (14%). The European Union (EU) contributed 10% of emissions. China’s emissions increased 5.9% between 2011 and 2012, whilst the USA and EU continued to decrease their CO₂ output (by 3.7% and 1.3% respectively).

CDIAC Data; Le Quiere et al 2013. Global Carbon Project 2013.

While developing nations like China and India have high levels of greenhouse gas emissions, it is important to note that per capita the USA has by far the highest emission rate at 4.4 tonnes of carbon per person per year (tC/p/yr). China has reached EU levels of 1.9 tC/p/yr, while India produces just 0.5tC/p/yr. Since the Industrial Revolution the USA and Europe still have the highest cumulative output of CO₂ from burning fossil fuels, something to consider before we become too self-righteous.

CDIAC Data; Le Quiere et al 2013. Global Carbon Project 2013.

Carbon sinks

Image by Manfred Heyde

Increased CO₂ emissions are absorbed by carbon sinks, specifically the atmosphere, the oceans and the land. On land, trees and other plants absorb around 27% of emitted CO₂ for photosynthesis, which results in more growth and eventually more carbon stored as leaf litter in the soil.

In the oceans, algae may absorb some CO₂ for photosynthesis (although not as much as was once hoped), but the water itself absorbs most of the 27% of CO₂ stored in the oceans. Unfortunately when carbon dioxide dissolves in water it can react to form carbonic acid, a leading cause of ocean acidification. Since the Industrial Revolution, oceans have become approximately 30% more acidic. If present trends continue, oceans will be 170% more acidic by 2100, a devastating change for shellfish and corals which rely on an alkaline calcium carbonate exoskeleton, and the other marine life that depend on these species.

The atmosphere absorbs the remaining 45% of CO₂ emissions. Over the past 250 years the atmospheric CO₂ concentration has risen from 227 parts per million (ppm) to an average of 393ppm in 2012. Back in May, the first CO2 reading of 400ppm was recorded, a significant milestone in the relentlessly increasing greenhouse gas levels. We are now on track to see a ‘likely’ 3.2-5.4°C increase in global temperature by 2100, causing severe droughts and desertification of agricultural land around the world and flooding of low lying coastal areas.

The Kyoto protocol

In 1992, 37 industrialised countries agreed to reduce their carbon dioxide emissions by an average of 5% below 1990 levels during the period of 2008 to 2012. The Global Carbon Budget reported that whilst some regions such as Europe did reduce their CO₂ output, other areas (eg. Asia, Africa, Middle East) doubled or even tripled their emissions, resulting in a net gain of 58% more CO₂ emissions in 2012 than in 1990.

The biggest CO₂ emitter, China, recently joined almost 200 other countries in agreeing to sign the pledge to reduce their carbon emissions at a summit in Paris in 2015. It is hoped that this climate change summit will follow on from the work started by the Kyoto protocol to reduce CO₂ emissions to a more sustainable level.

What’s your carbon footprint?

We are at a critical stage in history. The Global Carbon Budget suggests that we have already produced 70% of the carbon dioxide it is possible to emit without causing a significant and irreversible change to the planet’s climate. It is vital that all nations work together to reduce carbon emissions to a sustainable level, preventing a 2°C increase in global temperature.

If you would like to calculate your carbon footprint, visit the government’s carbon calculator.

This blog is written by Sarah Jose, Biological Sciences, University of Bristol

You can follow Sarah on Twitter @JoseSci

Sarah Jose

I work on an experiment that began when the Bee Gees’ Stayin’ Alive was at the top of the charts. The project is called AGAGE, the Advanced Global Atmospheric Gases Experiment, and I’m here in Boston, Massachusetts celebrating its 35-year anniversary. AGAGE began life in 1978 as the Atmospheric Lifetimes Experiment, ALE, and has been making high-frequency, high-precision measurements of atmospheric trace gases ever since.

At the time of its inception, the world had suddenly become aware of the potential dangers associated with CFCs (chlorofluorocarbons). What were previously thought to be harmless refrigerants and aerosol propellants were found to have a damaging influence on stratospheric ozone, which protects us from harmful ultraviolet radiation. The discovery of this ozone-depletion process was made by Mario Molina and F. Sherwood Rowland, for which they, and Paul Crutzen, won the Nobel Prize in Chemistry in 1995. However, Molina and Rowland were not sure how long CFCs would persist in the atmosphere, and so ALE, under the leadership of Prof. Ron Prinn (MIT) and collaborators around the world, was devised to test whether we’d be burdened with CFCs in our atmosphere for years, decades or centuries.

Fig 1. The AGAGE network

ALE monitored the concentration of CFCs, and other ozone depleting substances, at five sites chosen for their relatively “unpolluted” air (including the west coast of Ireland station which is now run by Prof. Simon O’Doherty here at the University of Bristol). The idea was that if we could measure the increasing concentration of these gases in the air, then, when combined with estimates of the global emission rate, we would be able to determine how rapidly natural processes in the atmosphere were removing them.

Fig 2. Mace Head station on the West coast of Ireland

Thanks in part to these measurements, we now know that CFCs will only be removed from the atmosphere over tens to hundreds of years, meaning that the recovery of stratospheric ozone and the famous ozone “hole” will take several generations. However, over the years, ALE, and now AGAGE, have identified a more positive story relating to atmospheric CFCs: the effectiveness of international agreements to limit gas emissions.

The Montreal Protocol on Substances that Deplete the Ozone Layer was agreed upon after the problems associated with CFCs were recognised. It was agreed that CFC use would be phased-out in developed countries first, and developing countries after a delay of a few years. The effects were seen very rapidly. For some of the shorter-lived compounds, such as methyl chloroform (shown in the figure), AGAGE measurements show that global concentrations began to drop within 5 years of the 1987 ratification of the Protocol.

Figure 3. Concentrations of methyl chloroform, a substance banned under the Montreal Protocol, measured at four AGAGE stations.

Over time, the focus of AGAGE has shifted. As the most severe consequences of stratospheric ozone depletion look like they’ve been avoided, we’re now more acutely aware of the impact of “greenhouse” gases on the Earth’s climate. In response, AGAGE has developed new techniques that can measure over 40 compounds that are warming the surface of the planet. These measurements are showing some remarkable things, such as the rapid growth of HFCs, which are replacements for CFCs that have an unfortunate global-warming side effect, or the strange fluctuations in atmospheric methane concentrations, which looked like they’d plateaued in 1999, but are now growing rapidly again.

The meeting of AGAGE team members this year has been a reminder of how important this type of meticulous long-term monitoring is. It’s also a great example of international scientific collaboration, with representatives attending from the USA, UK, South Korea, Australia, Switzerland, Norway and Italy. Without the remarkable record that these scientists have compiled, we’d be much less informed about the changing composition of the atmosphere, more unsure about the lifetimes of CFCs and other ozone depleting substances, and unclear as to the exact concentrations and emissions rates of some potent greenhouse gases. I’m looking forward to the insights we’ll gain from the next 35 years of AGAGE measurements!This blog was written by Dr Matt Rigby, Atmospheric Chemistry Research Group, University of Bristol.

Matt Rigby

Month: November 2013

Global carbon budget reveals dangerous footprints

35 years monitoring the changing composition of our atmosphere