Carbon dioxide, the greenhouse gas linked to global warming, is accumulating in the Earth's atmosphere at an increasing rate, according to a new study released by the US government's National Oceanic and Atmospheric Administration. The research has renewed concern that the ability of the environment to absorb the gas may be waning. The NOAA study said the average atmospheric concentration of carbon dioxide in 2005 reached 381 parts per million, up from 2.6 ppm since 2004. The annual rate of increase, which has been recorded since the 1950s, now exceeds 2 ppm for three of the past four years. This is an unprecedented increase; 50 years ago, the annual increase was less than 1 ppm.
The extra CO2 is produced by the burning of fossil fuels, currently emitting approximately 7 billion tons of carbon per year, and roughly half is absorbed by vegetation and the oceans. Researchers believe the yearly fluctuations in CO2 build-up are caused largely by nature's variable ability to absorb the emissions. The atmospheric concentration of carbon dioxide is now higher than experienced on Earth for at least the last 400,000 years, and the rise is expected to continue. Over the past two decades, only half of the CO2 released by human activities such as fossil fuel burning, the so-called ?anthropogenic CO2,? is still in the atmosphere; about 30% has been taken up by the ocean, and 20% by the terrestrial biosphere.
This new finding follows reports that 2005 was probably the warmest year on record, with temperatures slightly higher than the previous peak in 1998. Also, scientists at the US National Snow and Ice Data Center, in Boulder, Colorado, reported that Arctic sea ice did not reform fully in the winter of 2005 after record rates of melting during the summer.
Until recently the largest increases in concentrations of CO2 always occurred during El Ni'o years, when tropical vegetation grows more slowly due to lack of rain and fires occur in dried-out rainforests. The greatest recorded increase of 2.7 ppm occurred in the El Ni'o year of 1998. However, scientists are alarmed by the fact that none of the past three years of near-record increases have coincided with an El Ni'o event.
According to Peter Cox, a scientist at the Center for Ecology and Hydrology in Dorset, UK, who studies the interaction between plants and the atmosphere, the recent surge in CO2 levels ?may be the first evidence of a feedback from the carbon cycle, in which plants under heat stress from global warming start to absorb less carbon dioxide?.
Not only are plants slowing their rate of CO2 absorption, but coastal carbon sinks are shrinking as well. Mangrove forests, which play a large role in sequestering carbon from the atmosphere and dissolving it into the ocean, are disappearing rapidly. A research team led by Thorsten Dittmar of Florida State University in Tallahassee studied how much mangroves contribute to the organic carbon dissolved in ocean waters off the coast of Brazil. They came to the conclusion that even though intertidal mangrove forests cover only 0.1% of the earth's surface, they contribute up to 10 per cent worldwide of the ocean's dissolved organic carbon. This is approximately equal to the amount reaching the ocean from the Amazon river, the largest single source of dissolved organic carbon.
Intertidal forests of mangroves surround many tropical coastlines. Mangroves, like all plants, fix carbon dioxide from the atmosphere through photosynthesis and return organic material to the soil when they decompose. Their tangled root systems also collect fallen leaf litter. However, mangrove roots and soil are washed over by tides, and much of this organic carbon leaches into the ocean. Unlike CO2 absorbed directly from the atmosphere, much of the carbon produced by mangrove trees is bound up in large molecules which are highly resistant to decomposition, and is therefor likely to be held in the ocean for decades instead of being returned to the atmosphere as carbon dioxide.
Mangrove forests have declined by nearly fifty percent during the past century due to increasing coastal development and habitat damage, such as the draining of swamps for agriculture. As the habitat has changed, fewer mangrove trees and their derived detritus are available to bind and export dissolved organic matter into the ocean. The research team concluded that the rapid decline in mangrove forests threatens to shut off this important link in the carbon cycle, with potentially damaging consequences for atmospheric composition and climate.
Direct absorption of CO2 by the ocean surface also occurs, but it has unfortunate consequences not produced by complex carbon molecules fixed by plants. As dissolved CO2 rises, the pH of the ocean water decreases, becoming more acidic. This low pH causes the calcium carbonate shells of sea creatures to dissolve or form poorly, threatening coral reefs.
A pH reduction of approximately 0.1 unit in surface waters has occurred already due to oceanic uptake of anthropogenic CO2. Scientists estimate that the total drop in surface seawater acidity (pH) will be approximately 0.4 pH units by the end of this century, with an almost 50% increase in the concentration of dissolved carbonate ion concentration. The surface ocean pH drop would be lower than it has been for more than twenty million years.
Sometimes we need to think the unthinkable, particularly when dealing with a problem as dangerous as climate change - there is no room for dogma when considering the future habitability of our planet. It was in this spirit that I and a panel of other specialists in climate, economics and policy-making met under the aegis of the Stockholm Network thinktank to map out future scenarios for how international policy might evolve - and what the eventual impact might be on the earth's climate.
We came up with three alternative visions of the future, and asked experts at the Met Office Hadley Centre to run them through its climate models to give each a projected temperature rise. The results were both surprising, and profoundly disturbing. We gave each scenario a name. The most pessimistic was labelled "agree and ignore" - a world where governments meet to make commitments on climate change, but then backtrack or fail to comply with them. Sound familiar? It should: this scenario most closely resembles the past 10 years, and it projects emissions on an upward trend until 2045.
A more optimistic scenario was termed "Kyoto plus": here governments make a strong agreement in Copenhagen in 2009, binding industrialised countries into a new round of Kyoto-style targets, with developing countries joining successively as they achieve "first world" status. This scenario represents the best outcome that can plausibly result from the current process - but ominously, it still sees emissions rising until 2030.
The third scenario - called "step change" - is worth a closer look. Here we envisaged massive climate disasters around the world in 2010 and 2011 causing a sudden increase in the sense of urgency surrounding global warming. Energised, world leaders ditch Kyoto, abandoning efforts to regulate emissions at a national level. Instead, they focus on the companies that produce fossil fuels in the first place - from oil and gas wells and coal mines - with the UN setting a global "upstream" production cap and auctioning tradable permits to carbon producers.
Instead of all the complexity of regulating squabbling nations and billions of people, the price mechanism does the work: companies simply pass on their increased costs to consumers, and demand for carbon-intensive products begins to fall. The auctioning of permits raises trillions of dollars to be spent smoothing the transition to a low-carbon economy and offsetting the impact of price rises on the poor. A clear long-term framework puts a price on carbon, giving business a strong incentive to shift investment into renewable energy and low-carbon manufacturing. Most importantly, a strong carbon cap means that global emissions peak as early as 2017.
This "upstream cap" approach is not a new idea, and our approach draws in particular on a forthcoming book by the environmental writer Oliver Tickell. However, conventional wisdom from governments and environmental groups alike insists that "Kyoto is the only game in town", and that proposing any alternative is dangerous heresy.
But let's look at the modelled temperature increases associated with each scenario. "Agree and ignore" sees temperatures rise by 4.85C by 2100 (with a 90% probability); for "Kyoto plus", it's 3.31C; and "step change" 2.89C. This is the depressing bit: no politically plausible scenario we could envisage will now keep the world below the danger threshold of two degrees, the official target of both the EU and UK.
This means that all scenarios see the total disappearance of Arctic sea ice; spreading deserts and water stress in the sub-tropics; extreme weather and floods; and melting glaciers in the Andes and Himalayas. Hence the need to focus far more on adaptation: these are impacts that humanity is going to have to deal with whatever now happens at the policy level.
But the other great lesson is that sticking with current policy is actually a very risky option, rather than a safe bet. Betting on Kyoto could mean triggering the collapse of the West Antarctic ice sheet and crossing thresholds that involve massive methane release from melting Siberian permafrost. If current policy continues to fail - along the lines of the "agree and ignore" scenario - then 50% to 80% of all species on earth could be driven to extinction by the magnitude and rapidity of warming, and much of the planet's surface left uninhabitable to humans.
Billions, not millions, of people would be displaced. So which way will it go? Ultimately the difference between the scenarios is one of political will: the question now is whether humanity can summon up the courage and foresight to save itself, or whether business as usual - on climate policy as much as economics - will condemn us all to climatic oblivion.
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James Nash has sinced written about articles on various topics from Environment, Painting and Environment. James Nash is a climate scientist with Greatest Planet (). Greatest Planet is a non-profit environmental organization specialising in carb. James Nash's top article generates over 368000 views. to your Favourites.