Climate science in the spotlight

 

With global disputes on the decline, climate change has been identified as the greatest challenge for continued peace and long-term sustainability. Climate scientists are alarmed by human intervention in climatic processes. As the most ardent observers of the earth’s atmosphere, they feel responsible for sharing their concerns with the public. Speakers in this section present past discoveries and the latest scientific predictions on an accessible level.

CO₂ is not the strongest greenhouse gas, chlorofluorocarbons are. Nor does it contribute the most to the greenhouse effect, water vapor takes that honour. Climate science has singled out CO₂ because it enhances the greenhouse effect more than any other gas.

CO₂ is now considered a pollutant, and at 26 gigatonnes per year (4000kg for every person on earth) it is the largest waste stream we produce. Human activity only releases 5% as much CO₂ as earth’s systems circulate, but 57% of our emissions are beyond what can be absorbed. The result is a 0.5% increase in atmospheric CO₂ levels every year.1 As David Archer emphasizes, the carbon dioxide we emit stays in the atmosphere for 300 years on average, and one-quarter stays there for millennia.

The strong case for climate change due to human activity is based on just two facts. CO₂ in the atmosphere is correlated with surface temperature, and the rise in CO₂ levels is due to human activity. Anthropogenic (human-induced) climate change is not disputed by a single active scientist. As a hypothesis, the 2007 IPCC report assigns it a confidence level of 90% or greater, a number widely used in statistics.

Human emissions have to be decreased below the natural absorption rate in order to reduce atmospheric CO₂. Right now we emit double what earth’s systems can absorb. The consensus from climate science is that a 60-80% reduction in CO₂ emissions is needed to stabilize the CO₂ forcing.2 The challenge is to emit at 1955 levels with a population three times the size.

The greenhouse effect has a history that begins in 1829. CO₂ was recognized as a greenhouse gas in 1896 by Svante Arnhennius. He predicted that a doubling of CO₂ levels would result in a 4-6° heating.  With vastly improved models and a wealth of data the IPCC predicts a heating of 2-4.5° for a doubling of atmospheric CO₂.

The ‘first responder’ systems to absorb co2 are plant life and oceans. The oceans absorb the lion’s share, similar to their coverage of earth’s surface. Ocean uptake of CO2 is limited by the mixing of layers, while plant growth (both on land and in the oceans) is mostly limited by the availability of nutrients.3

We have unknowingly relied on the oceans to act as a CO₂ sponge; they have already absorbed half of our CO₂ emissions. New evidence shows that human activity is changing the pH of the ocean surface, stunting the growth of coral and other ocean life.4 Local stresses (nutrient loading) combined with global stresses (ocean acidification) are disrupting marine life in unpredictable ways.

Ecosystem services have an estimated value on par with global productivity, about $30 trillion. They depend largely on the state of the oceans, something we have scarce data on. The DSCOVR satellite was built to study the sun-exposed surface of the earth. It was set to become one of the best instruments for studying the climate, but its launch was delayed indefinitely.

More than a few unsupported claims have been put forth regarding climate modeling. One claim is that sun cycles affect the climate more than human activity. Gerard Bond describes in this brief video the size and nature of solar fluctuations, which are shown graphically here. The blog RealClimate puts the sun-climate effect at “about 10 to 15% the magnitude of the greenhouse gas forcing over the 20th Century.”5

For better or worse, the doom-and-gloom aspect of climatology gets a lot of attention. People often speak of climate ‘tipping points’, major events that would make severe climate change unstoppable. These events are not predictable with any level of confidence, but in the event of a five degree warming they are considered far more likely to happen. One of the main goals of curbing emissions now is to protect ourselves from these unpredictable events in the immediate future.

Continue to A climate of awareness to see how global engagement on climate change and a general interest in sustainability came about.

 

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