What IPCC’s climate report says about rising sea levels

Lauren Sommer, BURN Contributor

No one was too shocked by the latest climate projections released in the Intergovernmental Panel on Climate Change’s (IPCC) fifth report on Friday. The United Nations-created group is responsible for a sort of climate change “master doc,” collating studies from around the globe into a general consensus with the help of thousands of scientists.

 What did they find? Global temperatures are on the rise and we’re to blame. Or, in scientific speak, the panel said it’s “extremely likely” (greater than 95 percent certainty) that the warming is primarily due to human influence (burning fossil fuels and pumping carbon into the atmosphere). “There is a need for us to reduce emissions of greenhouse gases substantially if we really want to stabilize the Earth’s climate and I hope this is a message that the world will receive and accept,” said IPCC chairman Rajendra Pachauri.

IPCCchart1One topic did grab headlines: rising sea level. On average, it’s already gone up about seven inches since 1900, but the rate of change is expected to speed up. Under a worst-case scenario with unchecked greenhouse gas emissions, sea levels could rise 20 to 38 inches by the end of the century. That’s higher than the IPCC assessed in its last report six years ago, which put it from 10 to 23 inches.

Why the difference? It has to do with the two different factors that cause sea level rise. One is based on a basic tenet of physics: as water gets warmer, it expands. That’s caused about 40 percent of the sea level rise they can account for over the last decade.

The other cause of sea level rise is a little trickier for scientists to sort out. Glaciers and the Greenland and Antarctic ice sheets contain massive amounts of water, and they’re melting. That makes the ice sheets the “ticking time bombs” of climate change, according to some. Complete loss of the Greenland ice sheet, something the report says is possible with sustained warming over a millennium, would cause sea levels to rise by 23 feet.

IPPCchart2

The Greenland ice sheet is losing ice at a faster and faster pace, but in its previous report, the IPCC excluded some of that information from its sea level rise projections, saying not enough was known about the melting process to model it accurately. The state of the science has improved, the panel says, hence the jump in the numbers.

Other studies in the scientific community put sea level rise projections even higher. The IPCC acknowledged that, but found “there is no consensus currently in the scientific community about these very high sea level projections over the next 100 years,” according to Thomas Stocker, co-chair of the IPCC working group that released the report.

As was seen with Superstorm Sandy, the economic cost of storm surges and flooding runs into the billions and may only be a taste of what’s predicted for New York City and other places around the globe. More details about the sea level rise scenarios and the strategies to reduce carbon emissions are expected as the IPCC rolls out the rest of its assessment over the next year.

Lauren Sommer reports on environment, science and energy for KQED Public Radio in San Francisco. All graphics from IPCC.

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Alex Chadwick looks at the IPCC’s new report

Alex Chadwick, BURN Host

You’ll see a lot of climate news in the next few days. And maybe hear some climate shouting.

The Intergovernmental Panel on Climate Change (IPCC) has released its latest report. Founded 25 years ago by the UN, the IPCC is the principle world science organization reviewing data and studies on climate. This new report is the fifth since 1990. Each one concludes with increasing certainty that human influence is causing the world to warm, and that the effects of human activity will accumulate for decades and centuries, altering the planet in ways we have never seen.

A summary paper again shows increased confidence that greenhouse gases – mainly CO2 from burring carbon-based fuels – account for most of the warming that scientists have observed since the industrial age began 200 years ago. The last report said the IPCC was 90 percent sure of this conclusion – it is now said to be 95 percent sure. But a lot  more attention is probably going to explanations of something earlier reports did not completely foresee – what the IPCC calls “a pause” in the rise of average global surface temperatures over the last dozen or so years. The fundamental science of global warming is based on the earth retaining more energy and heat from the sun, much of which should reflect off the planet and back into space. If greenhouse gases are trapping that heat – and basic physics says they are – where is it?

A series of recent papers cited by the IPCC answers that – the heat is sinking into the ocean, especially the deep Pacific Ocean. There’s a pretty clear and accessible explanation for it at the site RealClimate, in an article by a German oceanographer, Stefan Rahmstorf. But climate skeptics are unlikely to be persuaded – the Pulitzer Prize winning site Inside Climate News reports they mean to seize on the reports findings to try to create more doubt. The data can look contradictory, especially for non-scientists: which set of facts do you believe?

Here’s some help from BURN contributor Richard Muller, a UC Berkeley physicist and noted former climate skeptic who changed his mind after an extensive three-year review of data. Writing in the New York Times this week, he compares climate trends to a staircase – that is, a series of risers and treads. Just because you reach a landing, he says, doesn’t mean the stairs stop going up.

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