Start the car, turn on the gas under the kettle, shovel some coal on the fire. Each time that happens, another pulse of carbon dioxide is released into the atmosphere − and in just 10 years, that newly-released gasp of greenhouse gas turns into global warming.
Scientists at the Carnegie Institution for Science in the US have calculated for the first time a precision figure for the average lag between a carbon emission and its effect on the planetary thermometer.
That there is a lag, no one ever doubted: thermal inertia is something everybody observes every time they put the kettle on. The heat goes up, but the water stays cold, for a while.
But the presumption has always been that – given that the world is a huge cauldron and every unit of fossil fuel burned represents a tiny increment – the time lag between cause and effect might be decades.That is, the warming experienced now was triggered by fossil fuel burning in the 1980s or 1990s.
But the two Carnegie scientists, Katharine Ricke and Ken Caldeira, report in the journal Environmental Research Letters that they have done the sums and arrived at a conclusion. People who light a gas cooker today are quite likely to feel the atmospheric heat from that blue flame in a decade.
Benefits here and now
Figures such as these come with a wide range of uncertainty. The calculations of the Carnegie team find a 90 per cent probability that the effect is felt between 6.6 years and 30.7 years, with a median time of 10.1 years. The effects of that one pulse might arrive in a decade, but would last for more than a century.
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Once carbon has been emitted into the atmosphere, the warming effect will last many centuries, even after much of the carbon has been absorbed by the oceans
Philip Goodwin, researcher at the University of Southampton’s National Oceanography Centre
“Amazingly, despite many decades of climate science, there has never been a study focused on how long it takes to feel the warming from a particular emission of carbon dioxide, taking carbon-climate uncertainties into account,” Dr Ricke said.
“A lot of climate scientists may have an intuition about how long it takes to feel the warming from a particular emission of CO2, but that intuition might be a little out of sync with our best estimates from today’s climate and carbon cycle models.” The effect measured by the two scientists is limited strictly to temperature, rather than longer-term consequences such as sea level rise or melting glaciers.
Research of this kind – as usual, based on climate models – has two ends: one is to arrive at a more precise understanding of the climate machinery. The other is to remind people that the consequences of any human action may be more immediate than anyone expected, which would be an encouragement to personal restraint and political concern.
“Our results show that people who are alive today are very likely to benefit from emissions avoided today and that these will not accrue solely to impact future generations,” Dr Ricke said.
Co-incidentally a team from three British universities report in Nature Geoscience that they have confirmed another basic link between carbon emissions and warning: the levels of greenhouse gases emitted are proportional to the levels of subsequent warming.
Given that the whole debate about climate change and fossil fuel emissions is predicated on such an outcome, this seems a bit tardy. But what Philip Goodwin, researcher at the University of Southampton’s National Oceanography Centre, and colleagues have done is based on computer simulations: they have derived a theoretical equation that makes a precision link between emissions and subsequent temperature, and then put a value on it.
Every trillion tonnes of carbon emitted will raise the planetary temperature by one degree Celsius. The same calculations confirm that, even if fossil fuel emissions are phased out altogether, the build-up of carbon over the last 200 years will keep the planet warmer for many centuries, or even millennia.
Research like this isn’t simple: it effectively explores the complex relationship between carbon dioxide levels in the atmosphere and the behaviour of the oceans. Like the Carnegie finding, it enriches scientific understanding of the climate machine. And it, too, makes a political point.
“Our analysis highlights the nearly irreversible nature of carbon emissions for global warming,” Dr Goodwin said. “Once carbon has been emitted into the atmosphere, the warming effect will last many centuries, even after much of the carbon has been absorbed by the oceans.”
