THE SCIENCE AND FACTS OF SEA LEVEL RISE
”When the facts change, I change my mind. What do you do, sir?”
-attributed to economist John Maynard Keynes
While researching this film, I have often felt that climate facts can appear as changeable as weather, and every few months or so I find I need an update. By now there is one fact that has been proven beyond reasonable doubt – that we humans are causing our planet to warmi ii iii. But almost every week there is new data and new research – new facts – about how fast and by how much this warming is happening.
I find my brain (and probably most people’s brain) struggles when it has to deal the scale and time frames of climate change. It is sometimes hard to see what is inevitable and what is still variable. Here’s a mental picture that I find helpful:
You’re in a sunny valley by a dry river bed. But you look up to the mountains and you see dark clouds forming over the peaks; rain. It’s still sunny in your valley, but you know that eventually the rain falling on the mountains will reach you and fill up the dry river bed. You know the water is not going to just stay on the mountain, and it certainly isn’t going to go uphill either: the water will run down the mountain pulled by gravity. It’s a force of nature, invariable. But what you can’t know for sure is how quickly that water reaches you, or how much water will flow in the river bed. These depend on many factors, some big and easy to predict (the slope of the mountain) and others very small and difficult to estimate (variations in the terrain, the ability of the ground to soak up water, evaporation etc). But if enough water falls, it is only a matter of time before it reaches you.
In global warming terms, it is raining on the mountain tops while it is still sunny in our valley. And it seems to be raining a lot. Forces of nature have been set into motion that will continue until they reach an equilibrium, and it is only a matter of time before we feel the effects of those forces. One of these effects is a rise in sea level.
Why sea level rises
Just as gravity is an undeniable force of nature, so too is heat expansion. Water expands with heat and it is just as true for the sea as it is for the water in a kettle.
As the atmosphere warms, most of that heat energy is taken up by the oceans, and as it warms the seas, so the water expands and the sea level risesiv. Because the atmosphere has already warmed the sea is rising and will continue to rise, and there is no way of stopping this – just like the rain running down the mountain. It is not a question of will the seas rise that is open for debate, but rather how much will the seas rise and how quickly.
About half of the projected sea level rise comes from heat expansionv. The other half of sea level rise comes from the melting of the large ice sheets (Greenland and Antarctica). The processes involved in the melting of these ice sheets is less well understood than thermal expansion, and so it is harder to predict how much the melting of this ice will affect sea level rise. However, both are affected by heat: a warmer atmosphere means more melting ice and more expanding water.
How much will the world warm by 2100?
Much depends on the amount of carbon pollution we will be releasing into the atmosphere over the next decades. Carbon pollution in the atmosphere in the form of CO2 acts like a warm blanket over the earth. The more carbon in the atmosphere the ”thicker” that blanket is and the hotter the world becomes. The tricky thing about carbon is once it is released its affect lingers for approximately one thousand yearsvi. One can’t just throw the blanket off – it will be up there for a very long time. Other important factors that determine warming is the planet’s ability to bounce back the sun’s energy off large white surface like ice and clouds, and the stability of the Arctic and Antarctic ice sheets.
A major milestone in climate science awareness was the Intergovernmental Panel on Climate Change (IPCC) report of 2007, a joint report written by over independent 2600 climate scientists. The report set out various scenarios for the global temperature trends depending on how much carbon pollution we release into the atmospherevii, e.g. scenario a) we would continue polluting as usual, scenario b) we would pollute until 2020 and then start limiting and so on. Most of the studies that have been used in recent years use one of these scenarios as a starting point, usually the ”moderate” one where we would gradually curb carbon emissions by mid-century.
A key political target has been to limit the amount off carbon in order to keep the world from warming by more than 2°C, a limit that most scientists considered ”safe”. This was the only thing that the Copenhagen Agreement (2009) could actually agree on.
However, at present there is no sign that we will be limiting carbon emissions anytime soon. On the contrary, since 2007 and 2009 we have burnt more fossil fuels and released more carbon than ever beforeviii ix. There is more carbon in the atmosphere (400ppm) than there has been for at least 800,000 years, way above the ”safe” limitx, but just stopping the rise in carbon pollution – not to mention bringing it back down to a safe level – would mean that we would have to immediately cut fossil fuels by 60%xi.
So it seems very unlikely that we would be able to limit warming to 2 °C by 2100. It is probably physically and politically impossible. Instead, we are on track for a temperature increase of anywhere between 2.4 and 6.4 °Cxii. So far, this track has followed the 2007 IPCC projections’ most pessimistic scenarioxiii, but even that scenario may be too conservative for the future.
For instance, Arctic sea ice loss is accelerating much faster than anyone could imaginexiv xv, and at the moment the polar region could be ice-free in the summers in less than 30 years, instead of after the year 2070 that was predicted only a few years agoxvi.
The arctic ice sheet is crucial to keeping the planet cool. The large white surface reflects the sun’s heat back into space, whereas the dark sea soaks up the heat – melting the ice even quicker (and expanding the water faster). This heat-soaking ability of a dark surface is a familiar phenomenon to those of us who live in northern latitudes: in the spring even a small patch of dark earth – or a leaf lying on the snow – will soak up the sun’s rays and quickly melt the surrounding snow.
As the world warms it also affects the stability of the Arctic and Antarctic ice sheets. These are massive amounts of fresh water ice that are perched on top of land masses. There is much debate about how stable they are – are they firmly ”anchored” to rocks and mountains below them or, as melt water gathers beneath them, could they suddenly slip off the land like ice off a sloping roof? At present climate models presume that they are stable and that the melting happens steadily rather than suddenly.
Sea level rise projection for Little Yellow Boots
Considering the upward trend of carbon pollution and accelerating sea ice lossxvii, I believe it is justified to assume that the higher projections of more recently published reports for sea level rise will be closer to the truth.
The 2007 IPCC report projected a sea level rise of between 18cm and 57cm by the year 2100xviii. Since then, more accurate data has been gathered and many new studies have been published that confirm that this projection is far too conservative.
At present, the projected sea level rise for 2100 is between 50-190 cmxix xx xxi xxii, with several studies setting the upper limit at around 140 cm. A recent study by the European Ice2Sea project expects a 69 cm sea level rise assuming a mid-level carbon pollution scenario with emission leveling off after 2070xxiii.
I will also include a storm surge sea level rise of about 2m, as storms and storm surges are likely to become more frequent with warming temperaturesxxiv. This is a very low level: the great North Sea storm of 1953xxv had a storm surge of 5.6 metres, and more recently hurricane Sandy a storm surge of 4.2 metres.
What will sea level rise mean for humans?
A one metre sea level rise does not sound like much, but it would cover a land area of about a million km2 – about three times the land area of Germany. Over one hundred million people would be displacedxxvi.
A 1-2 metre sea level rise would mean the complete disappearance of many Pacific nations, and also put large population centres at risk such as Miami, London, Hamburg, New York, Boston, Rotterdam, Venice and Shanghai. Some of these cities are already taking steps to protect themselves, but it is not reasonable to think that we would have the money to build walls and dykes everywhere.
For the EU alone, the economic cost of a 1 metre rise would be €156 billion per year by the 2080’sxxvii, the top losers being the Netherlands, Germany, France and the UK. And this figure does not take into account damage from the increasing number of storms.
Sea level rise is slow, sure and devastating. Even though the focus of this film is the end of this century, the sea level rise that we have set in motion now will continue for hundreds of years to come.
It will be a very different world that the Little Yellow Boots will walk on.
In Espoo on August 7th, 2013
i Abraham & Nuccitelli: Survey find 97% of climate science papers agree warming is man-made [http://www.theguardian.com/environment/climate-consensus-97-per-cent/2013/may/16/climate-change-scienceofclimatechange?guni=Article:in%20body%20link] The Guardian; 2013
ii Cook et al.: Quantifying the consensus on anthropogenic global warming in the scientific literature [http://iopscience.iop.org/1748-9326/8/2/024024/article] 2013
iv Nuccitelli et al.: Comment on Ocean heat content and Earth’s radiation imbalance. II. Relation to climate shifts [http://www.skepticalscience.com/docs/Comment_on_DK12.pdf ] 2013
vi Solomon et al.: Irreversible climate change due to carbon dioxide emissions
vii IPCC Climate Change 2007: Synthesis Report [http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf ] 2007
ix Andrew Freedman: Global Carbon Emissions Hit Record High, Report Finds [http://www.climatecentral.org/news/global-carbon-emissions-hit-record-high-15318 ] 2012
xi Fen Montaigne: Record 400ppm CO2 milestone ‘feels like we’re moving into another era’ [http://www.theguardian.com/environment/2013/may/14/record-400ppm-co2-carbon-emissions] 2013
xii IPCC Climate Change 2007: Synthesis Report [http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf ] 2007
xiii Rahmstorf et al: Comparing climate projections to observations up to 2011 [http://iopscience.iop.org/1748-9326/7/4/044035/article] 2012
xvi Overland & Wang: When will the summer Arctic be nearly sea ice free? [http://onlinelibrary.wiley.com/doi/10.1002/grl.50316/full] May 2013
xvii Blunden, J. et al.: State of the Climate in 2012. Bull. Amer. Meteor. Soc., 94 (8), S1-S238. [http://www.climate.gov/news-features/understanding-climate/state-climate-2012-highlights ] 2013
xviii IPCC Climate Change 2007: Synthesis Report [http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf ] 2007
xix Vermeer& Rahmstorf: Global sea level linked to global temperature [http://www.pik-potsdam.de/~stefan/Publications/Journals/vermeer_rahmstorf_2009.pdf), (http://wh.er.usgs.gov/slr/sealevelrise.html] May 2009
xx Rahmstorf et al: Comparing climate projections to observations up to 2011 [http://iopscience.iop.org/1748-9326/7/4/044035/article] 2012
xxi Real Climate: Sea-level rise: Where we stand at the start of 2013 [http://www.realclimate.org/index.php/archives/2013/01/sea-level-rise-where-we-stand-at-the-start-of-2013/] January 2013
xxii National Research Council: Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future. [http://dels.nas.edu/Report/Level-Rise-Coasts/13389] The National Academies Press, 2012
xxiv Grinsted et al.: Projected Atlantic hurricane surge threat from rising temperatures
[http://www.pnas.org/content/early/2013/03/14/1209980110] February 2013
xxv Wikipedia: North Sea flood of 1953 [https://en.wikipedia.org/wiki/North_Sea_flood_of_1953]
xxvi Li et al: GIS Analysis of Global Impacts from Sea Level Rise
xxvii Brown et al.: The Impacts and Economic Costs of Sea-Level Rise on Coastal Zones in the EU and the Costs and Benefits of Adaptation [http://climatecost.cc/images/Policy_brief_2_Coastal_10_lowres.pdf] September 2011