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How did the projections from the IPCC 3^rd and 4^th reports match up against recorded temps for the last decade?

WHO: Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Germany
Grant Foster, Tempo Analytics, Garland, Maine, USA
Anny Cazenave, Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Toulouse, France

WHAT: Comparing the projections from the IPCC 3^rd report in 2001 and the IPCC 4^th report in 2007 to the observed climate data to 2011

WHEN: November 2012

WHERE: Environmental Research Letters Vol 7, No. 4 (2012)

TITLE: Comparing climate projections to observations up to 2011

The IPCC. It is the favourite punching bag of climate deniers and conspiracy theorists alike, who all like to claim that the reports are faulty or flawed or incorrect. So these researchers decided with the 5^th Assessment Report due soon to go back to the 3^rd and 4^th reports, check what was in the projections and see how accurate they were on temperature rise and sea level rise. Kind of like a mid-term report card!

Five years ago, the CO₂ concentration and global temperatures were closely following the projections of the IPCC 3^rd report, and sea level rise was tracking along the upper limit of the uncertainty range. So where the sea level rise projections were plus or minus several millimetres a decade, the observed data was only on the plus side. How did the projections look with an extra five years of data?

The IPCC projections didn’t attempt to include the effect of solar variability, volcanic eruptions or El Niño in their temperature models because those things are random and therefore pretty impossible to predict in the future. The observed data was adjusted to remove the random variability from solar, volcanic and El Niño effects so that the researchers were comparing apples to apples when trying to assess the accuracy of the IPCC projections. For those playing at home, they used a multivariate correlation analysis (yeah, I love those too!).

The data adjustment removed the cold anomaly from the 1992/3 Mt Pinatubo eruption, and the ‘exceptionally high’ 1998 temperature maximum from the extreme El Niño event. The observed data showed warming of 0.3^oC from 1990 to 2011. The IPCC 3^rd report projected 0.2-0.4^oC warming to 2011 and the 4^th report projected 0.3-0.5^oC warming. So for temperature increases, the IPCC was pretty much spot on.

3rd report projections in blue, 4th report projections in green, observed data in red, shaded areas are the uncertainty range. (from paper)

So what about sea level rise? The IPCC got that one wrong, but not in a way that climate deniers can celebrate – they underestimated it by 60%.

Sea level rise: measured data in red, third assessment in blue, fourth assessment in green (from paper)

The IPCC best assessment was 2.0mm per year of sea level rise, and the satellite based recorded data is actually 3.2mm per year (±0.5mm error range). The researchers tried to work out if the huge difference between the projection and the recorded data was because of variability over recent decades, and decided it was unlikely because the IPCC similarly underestimated the sea level rise from 1961-2003. It was even more unlikely because the rate of sea level rise over the past 130 years has a ‘highly significant correlation with global temperature’.

This is scientist for almost identical, because those of you that read the IPCC 3^rd report will remember that when the IPCC says ‘very likely’ they mean there’s a 90-99% chance it will happen. Talk about understatement.

What did the IPCC miss for sea level rise? Well firstly, it’s worth mentioning that most of the world’s scientific community didn’t expect humanity to ignore them when they warned of climate change, so their predictions were more conservative as they hoped we wouldn’t keep burning carbon at greater and greater rates as we are currently doing.

The key part though is ‘future rapid dynamical changes in ice flow’ which is scientist for big and unexpected changes, like the Arctic Death Spiral we had this summer where they found the Arctic was melting about 80 years ahead of schedule. The Arctic wasn’t supposed to be ice free in the summer from climate change until 2100, but we might get to see it as early as 2020.

What does that mean for future climate change projections? Well, it’s not pretty. So far the IPCC has been either seriously accurate (yay science!) or their worst case scenario underestimated what we’re actually doing to the planet. Which means that while the picture that the IPCC paints doesn’t look very appealing, it seems that reality could be a whole lot worse. My suggestion once again is that we stop burning carbon.

Brisbane floods 2011 (photo: Eric Veland, flickr)

WHO: Kunshan Gao, Guang Gao, Yahe Li, Bangqin Huang, LeiWang, Ying Zheng, Peng Jin, Xiaoni Cai, Wei Li, Kai Xu, Nana Liu (State Key Laboratory of Marine Environmental Science, Xiamen University, China)
Juntian Xu (School of Marine Science and Technology, Huaihai Institute of Technology, Lianyungang, China)
David A. Hutchins (Marine Environmental Biology, Department of Biological Sciences, University of Southern California, Los Angeles, California)
Donat-Peter Häder (experimental design and data analysis, Möhrendorf, Germany)
Ulf Riebesell (Helmholtz Centre for Ocean Research Kiel (GEOMAR), Kiel, Germany)

WHAT: Large project in the South China Sea to work out the effects of increased CO₂ on important algae

WHEN: July 2012

WHERE: Nature Climate Change, Vol 2 Issue 7 2012

TITLE: Rising CO2 and increased light exposure synergistically reduce marine primary productivity (sub required)

The bottom of the food chain contains the unsexy and somewhat unpopular plants and animals. Let’s face it, most of us are not going to get as worked up over algae as a really cute polar bear. But climate change is going to affect the algae too, so this large project between the State Key Laboratory of Marine Environmental Science in China, the University of Southern California and a centre for ocean research in Germany set out to find out what increased CO₂ levels mean for phytoplankton.

Phytoplankton – not as cute as polar bears (Logical Progressions, Flickr)

Phytoplankton are microscopic plankton that we can only see when there’s too many of them and they create an algal bloom. They are part of a larger group of algae, which are the building blocks of the food chain in the ocean and undergo photosynthesis (just like plants do) to create 40% of the primary production (really basic organic compounds) in the ocean.

So while they may not be the coolest things in the ocean, they’re pretty important.

Oceans absorb a really large amount of the carbon pollution we’re currently putting into the atmosphere – around 1millon tonnes of CO₂ every hour is absorbed and a quarter of that gets removed from the atmosphere and stored in the ocean. The increasing amount of carbon pollution we’re creating means more and more CO₂ is getting absorbed by the ocean, making the ocean more acidic.

Phytoplankton algal bloom in the Ross Sea, Antarctica (NASA Goddard Photo and Video, Flickr)

Acidic oceans are not fun for the local residents. Acid makes shells thinner and reduces the defences of animals that have them, and it bleaches coral, turning the coral white. So, if we ignore the need to reduce carbon pollution and allow 800 – 1000 parts per million (ppm) of CO₂ to collect in the atmosphere by 2100, what’s that going to do to the ocean and the algae?

That much atmospheric CO₂ will increase ocean acidification by 100- 150% (depending on how much we pollute and interactions with other bio-systems), which is really going to suck if you’re a shell-wearing animal or you hide in coral. It’s also going to affect the ability of phytoplankton to grow and therefore produce the basic organic compounds the ocean needs.

The researchers did controlled lab tests with different levels of CO₂ concentrations in sea water (between 390ppm which is what the world is currently at and 1000ppm) and different strengths of sunlight. They then checked these against the experiments conducted in the ocean to make sure their results were realistic.

To a certain point, the increased sunlight and CO₂ helps the phytoplankton grow, but beyond that point, the phytoplankton start getting stressed, and in extreme situations even start emitting carbon at night after absorbing it during the day.

Apart from the fact that humanity is really in trouble at the point where the ocean starts releasing carbon rather than storing it for us, an ocean where the building block organisms are stressed isn’t going to be very productive for growing things or living.

Higher CO₂ can reduce the ability of phytoplankton to grow by up to 81% depending on how much you stress them, but the more CO₂ is present, the less sunlight it takes to stress the phytoplankton and reduce their growth. The decrease in phytoplankton also saw an increase in Haptophytes, which form toxic algal blooms.

The effects of CO₂ on the phytoplankton can be kept neutral, but only if the amount of sunlight is kept under 30%, which is impossible outside of a lab. The researchers were not able to work out how these effects on phytoplankton would relate to CO₂absorption and sequestration in the ocean, or food production for the rest of the food chain. However, in a world where we allow 800- 1000ppm of CO₂ into the atmosphere, there’s unlikely to be any humans around either, since beyond around 450ppm irreversible positive feedbacks kick in and make our planet seriously non-linear (unpredictable and extreme).

So obviously for our sakes and for the poor phytoplankton too, we should reduce our carbon emissions and not let that happen.

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Tag Archives: oceans

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