Monthly Archives: July 2013

CO2 garden steroids

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Is additional atmospheric CO2 fertilizing plants? Is this a good thing?

WHO: Randall J. Donohue, Tim R. McVicar, CSIRO Land and Water, Canberra, ACT, Australia
Michael L. Roderick, Research School of Biology, Australian National University, Canberra,
Research School of Earth Sciences, Australian National University, Canberra,  Australian Research Council Centre of Excellence for Climate System Science, Sydney, New South Wales, Australia.
Graham D. Farquhar, Research School of Biology, Australian National University, Canberra, ACT, Australia.

WHAT: Trying to measure the effect that CO2 fertilization has on plants from increased atmospheric CO2 from global warming

WHEN: 19 June 2013

WHERE: Geophysical Research Letters, Vol. 40, Issue 12, June 2013

TITLE: Impact of CO2 fertilization on maximum foliage cover across the globe’s warm, arid environments (subs req.)

Climate deniers and people who don’t want to take action on climate change often say that increased levels of CO2 in our atmosphere will be a good thing, because plants need CO2 to grow, so why not let the plants have all the CO2 they want and watch them grow like gangbusters!?

More CO2= good? (Chris Gin, flickr)

More CO2= good? (Chris Gin, flickr)

This is the same as suggesting that because humans need water that I should drink water all the time without pause and that would be awesome (it wouldn’t; I would die from water intoxication). Flaws in denier logic aside, these researchers from the CSIRO tried to find out if you could measure whether there was an increase in plant growth from increased atmospheric CO2 and whether you could measure it.

The researchers looked at warm, arid areas of the world where rain is the limiting factor for plant growth. Places like South Western Australia, Southern California and South Eastern Spain. They then looked at the plant growth data from 1982-2010 and broke it into three year segments that were averaged to make sure they accounted for a lag time between changes in rain patterns and plant growth.

Warm arid areas included in the study (yearly data in grey, 3yr averages in red, from paper)

Warm arid areas included in the study (yearly data in grey, 3yr averages in red, from paper)

Then they ran the numbers for what plant growth would have been with constant amounts of rain so they could separate out the effect of CO2 alone.

What they found was that transpiration and photosynthesis are directly coupled to atmospheric CO2, which plays a role in setting the Fx edge (upper limit of plant growth). Plant growth increased ~11% between 1982 and 2010 from increased levels of atmospheric CO2 fertilization.

Then, just to make sure they were correct, they looked at the different things that could have influenced that increase. Increased temperatures lowered plant growth (too hot to grow). Plant productivity increased to a certain point under drought conditions (as plants became more water efficient and drought tolerant), but that couldn’t account for the 11% increase. There was an observed 14% increase in plant growth from a 10% increase in precipitation, but that couldn’t account for their numbers either because they ran them for a constant level of rain.

So, as the researchers stated in their paper, this ‘provides a means of directly observing the CO2 fertilization effect as it has historically occurred across the globe’s warm, arid landscapes’.

But does this mean all plants will grow more and we don’t have to worry about climate change anymore? Unfortunately, no.

This only applies to warm arid areas where water is the dominant limit to growth. Also, the other effects of climate change – longer droughts, more extreme storms, longer heatwaves, more extreme bushfires – are likely going to outweigh the positive effect of the increase in growth from CO2 fertilization.

The researchers point out in their conclusion that this research doesn’t simply translate to other environments with different limitations. In a Q&A with the CSIRO when asked whether this research means that climate change is good, the lead author Dr. Donohue stated; ‘this does not mean that climate change is good for the planet.’

So yes, there is a fertilization effect from increased CO2, but no, it doesn’t mean we get to keep burning carbon.

Extreme Overachiever Decade 2001-2010

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The World Meteorological Organisation global climate report for last decade shows it winning all the most extreme awards.

WHO: The World Meteorological Organisation (WMO) in conjunction with these international experts and meteorological and climate organisations.

WHAT: The Global Climate Report for the decade 2001-2010

WHEN: July 2013

WHERE: Online at the WMO website

TITLE: The Global Climate 2001-2010 A Decade of Climate Extremes (open access)

The World Meteorological Organisation (WMO) recently released their wrap up of the last decade’s worth of global weather related data. Now, as you will all remember, climate is the long term trend of the weather (generally over a 30 year period) but it’s also important to keep track of the decade to decade trends, if not because 10 is a nice round number to deal with.

So what did the last decade’s report card look like? Turns out 2001-2010 was an overachiever when it came to records and extremes, which is bad news for all of us, really. The last decade was the warmest on record for overall temperatures and the speed of warming has amped up as well. The long term warming trend is 0.062oC/decade, but since 1970 it’s sped up to 0.17oC/decade.

Decade by decade temperature record (from report)

Decade by decade temperature record (from report)

If you only look at land surface temperatures 2007 held the record for hottest with 0.95oC above average, with 2004 the ‘least warm’ (there’s no long term cold records happening here) at 0.68oC above average.

If you look at sea surface temperatures, 2003 wins with 0.40oC above average and 2008 was the least warm at 0.26oC above average. The warmest year in the Northern Hemisphere was 2007 at 1.13oC above average and in the Southern Hemisphere 2005 wins with 0.67oC.

When it comes to rain, it’s a mixed bag. There were places that got more rain, there were places with drought, there were more extremes. South America was wetter than normal, Africa was drier than normal. Overall, 2002 was the driest year of the decade and 2010 was the wettest. The problem with rain patterns changing with climate change is that the location and the time frame changes. Instead of slow soaking rains, it’s extremes of dry spells followed by flash flooding.

The patterns of El Niño and La Niña switched back quite a lot during the decade, with El Niño generally creating warmer trends and La Niña creating cooler trends.

El Niño and La Niña trends for sea surface temperatures (from report)

El Niño and La Niña trends for sea surface temperatures (from report)

To qualify as an extreme event, an event needs to result in 10 or more people dying, 100 or more people being affected, a declaration of a state of emergency and the need for international assistance, which I think is a pretty high bar. But of course, since the last decade was overachieving, there were 400 disasters of this scale that killed more than 1million people.

Weather disasters represented 88% of these extreme events and the damage from these events have increased significantly as well as seeing a 20% increase in casualties from the previous decade. The extra casualties have been from some extreme increases in certain categories like heatwaves. In 1991-2000 6,000 people died from heatwaves. In 2001-2010 that jumped to 136,000 people.

The price of extreme weather events has also gone up with 7,100 hydrometeorological events carrying a price tag of $US1trillion and resulting in 440,000 deaths over the decade. It’s also estimated that 20million people worldwide were displaced, so this was probably our first decade of a sizable number of climate refugees. Internal displacement will be one of the biggest factors as people move away from the more extreme parts of their country to the places where it still rains (eg. from Arizona to Oregon).

Tropical storms were a big issue, with the report noting ‘a steady increase in the exposure of OECD countries [to tropical cyclones] is also clear’. It’s nice to see them point out that issues around extreme weather are not a developing world problem because they don’t have the infrastructure to deal with them, shown through the flooding in Germany and Australia last decade.

There was also a special shout-out to my homeland of Australia, for the epic heatwave of 2009 where I experienced 46oC in Melbourne and can attest to it not being fun. Of course, that epic heatwave was beaten by 2013’s new extreme map colour. However I noted Australia was getting pretty much all of the extreme weather effects over the decade. Ouch.

Australia – can’t catch a break (compiled from report)

Australia – can’t catch a break (compiled from report)

Even for the category of ‘coldwaves’ where the Northern Hemisphere saw an increase in freak snowstorms, the average temperature for the winter was still +0.52oC warmer than average.

Last decade was also setting lots of records in the cryosphere (frozen part of the planet). 2005-2010 had the five lowest Arctic sea ice records which have been declining in extent and volume at a disturbingly rapid rate in what is commonly known as the Arctic Death Spiral. There’s been an acceleration of loss of mass from Greenland and the Antarctic ice sheets and a decrease in all global glaciers.

Arctic Death Spiral (from report)

Arctic Death Spiral (from report)

The World Glacier Monitoring Service describes the glacier melt rate and cumulative loss as ‘extraordinary’ and noted that glaciers are currently so far away from their equilibrium state that even without further warming they’re still going to keep melting. Oh, and last decade won the record for loss of snow cover too.

Declining snow cover (from report)

Declining snow cover (from report)

Sea level has started rising faster at a rate of 3mm/yr last decade, which is double the historical average of 1.6mm/yr. Interestingly, sea level rise is not even across the globe due to ocean circulation and mass. In a La Niña year, the Western Pacific Ocean can be 10-20cm higher than the average for the decade, but there’s only one way sea levels are going as the water warms and expands and the ice sheets melt – up.

Sea level rise (from report)

Sea level rise (from report)

Finally, if all of that wasn’t enough bad news for you – the report looked at the gas concentrations in the atmosphere and found (surprise, surprise) that CO2 is up and accounts for 64% of the increase in radiative forcing (making our planet warmer) over the past decade and 81% of the increase in the last five years. Methane is responsible for 18% of the increase and Nitrous Oxides chip in 6%.

Does it make anyone feel better if I tell you the hole in the ozone layer isn’t getting bigger anymore?

Basically the world we live in is getting more extreme as it heats up at an ever increasing rate. Given that these are the changes we’re seeing with a 0.8oC increase in global average temperatures and that’s from carbon we burnt over a decade ago, how about we stop burning carbon with a little more urgency now?

Your odds just shortened – Aussie Heatwaves

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Climate change has increased the chance of extreme heatwaves in Australia by more than five times.

WHO: Sophie C. Lewis and David J. Karoly, School of Earth Sciences and ARC Centre of Excellence for Climate System Science, University of Melbourne, Victoria, Australia

WHAT: Looking at how much influence human-caused climate changes are pushing Australian summers into more extreme heat.

WHEN: July 2013

WHERE: Geophysical Research Letters (DOI: 10.1002/grl.50673), pre-publication release

TITLE: Anthropogenic contributions to Australia’s record summer temperatures of 2013 (subs. req)

There’s some interesting research happening at my alma mater Melbourne University these days (go Melbourne!). Even if you weren’t there to experience the extreme summer of 2012-13 in Australia, I’m sure you all remember the new colour that had to be created by the Australian Bureau of Meteorology for the weather maps when they maxed out above 50oC, or maybe the new rating for bushfires of ‘catastrophic’ for the climate fuelled fires that are beyond just an extreme risk?

Extreme Heat in January 2013 (Bureau of Meteorology)

Extreme Heat in January 2013 (Bureau of Meteorology)

So, to answer that age-old question ‘exactly how much have we messed this up?’ these researchers looked at the historical monthly weather patterns, weather patterns with natural forcing only and patterns with natural forcing and human forcing and matched those up with what actually happened.

They looked at the average monthly mean temperatures, maximum temperatures and minimum temperatures and found that the monthly extremes are increasing faster than the daily extremes – that is that there are more months that are more overall extreme than there are days of extremes.

The historical data they used for the experiment was from 1850 to 2005, with the baseline climate data (what they used as a reference for ‘normal’) being 1911-1940 because 30 years of weather data makes a climate!

They then created experiments for the data with natural forcing only, with natural and human forcing and ran exciting statistical functions like a probability density function with a kernel smoothing function that almost sounds like a super-cool popcorn maker.

To double check for error, they used the second hottest summer temperatures to make sure they could pick out the human influences from the randomness that can be the data, thereby deliberately making their findings conservative.

Once they’d run their fun popcorn-sounding numbers, they calculated the FAR – Fraction of Attributable Risk, which is exactly what it sounds like – the fraction of the risk of something happening that can attributed to a cause.

So if our ‘bad guy’ is human-induced climate change, how much can we blame it for the Australian Angry Summer of 2012-13? Well, a fair bit.

When they compared the numbers, they had 90% confidence that there was a 2.5 times increase in extreme heat from human influences. When they compared 1976-2005 data and extended the model out to 2020, the fraction increased again to a 5 times increased likelihood.

Extreme heat is ‘substantially more likely’ because of humans burning fossil fuels, which are pretty bold words from research scientists – when there’s a greater than 90% chance of something they say ‘very likely’ where most people would say ‘very certain’. In their research, events that should have been occurring 1-in-16 years naturally were happening 1-in-6 years with the historical numbers and 1-in-2 years with the model out to 2020. Ouch – summer just got more uncomfortable more often.

MTSOfan, flickr

MTSOfan, flickr

For me, the kicker came when the paper pointed out that the 2012-13 summer in Australia came in a La Niña year. Extreme heat events normally come with an El Niño year – La Niña years are cooler with more rain. So the fact that the Angry Summer occurred in a La Niña year is scary – sea surface temperatures were average or cooler in some places while at the same time the Bureau of Meteorology was scrambling for new map colours.

The paper concludes that their research supports ‘a clear conclusion that anthropogenic climate change had a substantial influence on the extreme summer heat over Australia’ and that these kinds of events are now five times as likely to occur. Welcome to summers on climate change?

Drought – worse than we thought

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Inconsistencies with drought models that don’t account for sea surface temperature changes mean that drought in a climate changed world could be worse than predicted.

WHO: Aiguo Dai, National Center for Atmospheric Research, Boulder, Colorado, USA

WHAT: Looking at the impact of sea surface temperature variability on drought

WHEN: January 2013

WHERE: Nature Climate Change, Vol. 3, No. 1, January 2013

TITLE: Increasing drought under global warming in observations and models (open access)

Climate deniers love it when the models are slightly wrong for predicting future climate changes, and believe me, I’d love it if climate change weren’t so verifiably real and we could all retire and live la dolce vita.

However, that’s not reality, and in the case of this paper, where the model doesn’t quite line up with the observed changes that’s because it’s worse than we previously though. Oh dear.

Global warming since the 1980s has contributed to an 8% increase in drought-ridden areas in the 2000s. It’s led to things like diminished corn crops and the steady draining of underground water aquifers in the USA, much of which is currently experiencing persistent drought. The letter L on the map below stands for long term drought.

Long term drought in the Southwest of the USA (from US Drought Monitor)

Long term drought in the Southwest of the USA (from US Drought Monitor)

What’s that got to do with climate models? Well, while the droughts in Southern Europe or my homeland of Australia are due to lack of rain drying things out, drought can also be from increased evaporation from warmer air temperatures, which the models don’t fully take into account.

These droughts are harder to measure because they’re related to sea surface temperature changes that take decades and can be hard to identify as a human forced signal rather than just natural variations. So this researcher compared sea surface temperatures with drought predictions and observed warming to try and work out what is going on.

Predicted changes in soil moisture globally for 1980–2080 (black dots are where 9 out of 11 models agree on data) (from paper)

Predicted changes in soil moisture globally for 1980–2080 (black dots are where 9 out of 11 models agree on data) (from paper)

There were two areas where the models differed from the observed changes – the Sahel area in Africa and the USA.

In the Sahel, the models predicted there would be warming in the North Atlantic Ocean which would lead to increased rain. What actually happened was that there was large warming in the South Atlantic Ocean compared to the North Atlantic and steady warming over the Indian Ocean which meant less rain, not more. Similarly, for the predicted patterns in the USA, the influence of the Pacific Multidecadal Oscillation was not known to be influenced by human climate forcing. However, it switched to a warm phase from above-normal sea surface temperature.

Top: Observed sea surface temperatures. Bottom: predicted sea surface temperatures (from paper)

Top: Observed sea surface temperatures. Bottom: predicted sea surface temperatures (from paper)

These sea surface variations that were missed in some of the previous models have some obvious consequences for planning for the slow pressure cooker of stress that drought is on anyone living through it, let alone trying to make a living from agriculture.

The researcher noted that there were also some differences from the models when looking at sulphate aerosols, however for the 21st Century the signal from greenhouse gases will be much stronger than those from aerosols, so shouldn’t mess with the data too much.

So what does this all mean? Well, it means that there are both regional and broader trends for drought in a changed climate. The broad patterns are fairly stable ‘because of the large forced trend compared with natural variations’, which is scientist for humans are making a large enough mess out of this to see the evidence clearly.

The paper ends quite bluntly stating that having re-worked the simulations to take into account the new data for sea surface temperature and other variables, that it’s only more bad news.

It’s likely to be ‘severe drought conditions by the late half of this century over many densely populated areas such as Europe, the eastern USA, southeast Asia and Brazil. This dire prediction could have devastating impacts on a large number of the population if the model’s regional predictions turn out to be true.’

Yes, a researcher actually used the word ‘dire’ in a scientific paper. Oh, and this was with an intermediate emissions scenario, not the business as usual path we’re currently all on. How about we all agree to stop burning carbon now?