While politicians have effectively dithered on robust action to reduce greenhouse gas emissions over the last 20 years we are hearing more about geo-engineering proposals to moderate rising temperatures. But the latest study from the University of Reading scientists modelling solar radiation management, and in particular atmospheric aerosol injection - one of the easiest geo-engineering proposals to do at large scale - says such a project would result in a major decrease in tropical rainfall and an increase in drought in many regional areas.
The Reading University study concentrated on the consequences on geo-engineering methods to change the solar radiation reaching the earth: through mirrors above the atmosphere; and injecting sulfate aerosols into the atmosphere to reflect solar radiation. The first could prove hideously expensive and is at the moment impractical, but the second method is quite achieveable at reasonable cost.
The study - Weakened tropical circulation and reduced precipitation in response to geoengineering (Full paper) - looks at aerosol injection in particular and the projected impacts. It was published in Environmental Research Letters.
Related: Yale Environment360: Solar Geoengineering: Weighing Costs of Blocking the Sun’s Rays (9 Jan 2014)
The models were run to simulate four climates, including a 20th century control and a simulation with quadrupled CO2 concentrations ('4CO2') for both sulfate aerosol injection ('4CO2 + Sulfate') and solar dimming ('4CO2 + Solar').
One of the study co-authors, Angus Ferraro, commented:
"Previous predictions of how stratospheric aerosol injection would affect climate were based on a number of assumptions. By actually modelling what would happen if aerosol were to be pumped into the atmosphere around the equator, we have revealed a new impact of geo-engineering on tropical climate. As well as reflecting some of the incoming energy from the sun and cooling surface temperature, the aerosol also absorbs some of the heat energy coming from the surface which warms the stratosphere. We have shown for the first time that warming the stratosphere makes the troposphere below more stable, weakening upward motion and reducing the amount of rainfall at the surface."
The IPCC Fifth assessment report on the physical science also raised issues with geoengineering with both Carbon Dioxide Removal technologies and Solar Radiation Management:
"Methods that aim to deliberately alter the climate system to counter climate change, termed geoengineering, have been proposed. Limited evidence precludes a comprehensive quantitative assessment of both Solar Radiation Management (SRM) and Carbon Dioxide Removal (CDR) and their impact on the climate system. CDR methods have biogeochemical and technological limitations to their potential on a global scale. There is insufficient knowledge to quantify how much CO2 emissions could be partially offset by CDR on a century timescale. Modelling indicates that SRM methods, if realizable, have the potential to substantially offset a global temperature rise, but they would also modify the global water cycle, and would not reduce ocean acidification. If SRM were terminated for any reason, there is high confidence that global surface temperatures would rise very rapidly to values consistent with the greenhouse gas forcing. CDR and SRM methods carry side effects and long-term consequences on a global scale."
Some basics of geoengineering
Geo-engineering projects fall into two major categories: solar radiation management and carbon sequestration or carbon sink management (See wikipedia list).
Some of the proposals for aerosol injection have been brought to the fore by Professor Paul Crutzen in his 2006 paper - Albedo Enhancement by Stratospheric Sulfur Injections: A Contribution to Resolve a Policy Dilemma? PDF - that geo-engineering may be necessary to moderate temperature increases. (See also: Responding to Paul Crutzen)
Harvard scientist David Keith argues that aerosol injection is very feasible in the article - A Cheap and Easy Plan to Stop Global Warming, but has strong reservations about the technology particularly in regard to the moral hazard argument: Knowledge that geoengineering is possible makes climate impacts look less fearsome, with a weaker commitment to cutting emissions now.
Watch David Keith's 2007 TED talk on youtube:
In March 2010 Friends of the Earth (UK) become one of the first environmental NGOs which adopted a policy supporting further research on some geoengineering strategies (a Plan B) but also condemning "the lack of action by rich countries to significantly reduce carbon emissions since they signed the UN Climate Convention in 1992, and indeed from the 1970s and 80s when politicians were warned about the danger of carbon emissions to the climate." The 2009 policy brief (PDF) urged that Mitigation has to be the priority for action, and stating:
Large amounts of chemical air capture of carbon and storage – funded and carried out by rich countries – will probably be necessary, as long as safe storage sites can be identified and governance issues addressed. This should be in addition to significant reduction in emissions. Research into increasing the albedo effect of clouds is worth carrying out but not at the cost of mitigation or more promising air capture techniques, and only once a governance regime is agreed.
Friends of the Earth opposes injection of aerosols. We also currently oppose the large-scale use of afforestation, biomass with carbon capture and bio-char until land use competition issues with food production and biodiversity are solved. And we oppose the GM modification of plants to enhance the albedo affect due to the unknown risks associated with GM technologies.
Carbon sink geoengineering options should not be included within carbon markets because they are not yet proven to work over the necessary timeframe (thousands of years), also doing so would distract from mitigation which is the priority. Solar radiation geoengineering does not reduce carbon levels and therefore cannot be included in carbon markets.
In 2009 over 80 Civil society groups (the ETC Group) from around the world condemned plans being put to climate scientists meeting in Copenhagen regarding geo-engineering the earth as a fix for climate change.
In early October 2012 a $2.5 million project by Mr. Russ George was initiated for large-scale iron fertilization undertaken in the ocean off the coast of Haida Gwaii (British Columbia, Canada) – apparently in international waters to address the impacts of climate change on salmon. There was little scientific oversight and evaluation reported Greenpeace.
Geo-politics and regulation of geo-engineering
The technology to start injecting sulfate aerosols into the atmosphere is fairly basic and within the capability of any country to initiate. But we have no international agreements at the moment that could regulate this activity.
This raises the potential for geo-political conflict. It would be relatively easy for one developing nation or small island state to initiate sulfate aerosol injection into the atmosphere if they felt their population was unduly suffering from the impacts of climate change and may benefit from the geo-engineered climate. Countries in northern Europe and parts of Asia would be most likely to benefit, at the expense of parts of Africa, North and South America and South-East Asia.
As Professor Neville Nicholls from School of Geography and Environmental Sciences at Monash University made clear in this youtube video in October 2013, some geo-engineering has already taken place (ocean fertilisation). "It has major governance issues. Major problems of international law. But it is happening." he said.
In paraphrasing and elaborating on John Holdren, President Obama's chief science advisor, Nicholls said that you can do four things about climate change: you can mitigate and reduce emissions, you can adapt, you can geo-engineer, or suffer. "My feeling is we will do all four ... If a small island state decides to do stratospheric injection of aerosols, who is going to stop them?" he said.
The example of Large volcanic eruptions
Volcanic eruptions like Mount Pinatabo in the Philippines in 1992 inject sulfate aerosols high into the atmosphere which have a measurable effect. The year after Mount Pinutabo erupted global average temperatures decreased by up to 0.5C. Scientists concluded in a study on The Atmospheric Impact of the 1991 Mount Pinatubo Eruption that:
Effects on climate were an observed surface cooling in the Northern Hemisphere of up to 0.5 to 0.6°C, equivalent to a hemispheric reduction in net radiation of 4 W/m2, and an overall cooling of perhaps as large as -0.4°C over large parts of the Earth in 1992-93. Climate models appear to have predicted the cooling currently occurring with a reasonable degree of accuracy. The Pinatubo climate forcing was stronger than the opposite, warming effects of either the El Niño event or anthropogenic greenhouse gases in the period 1991-93.
But it was also noted that "mid-latitude ozone abundance reached its lowest level on record during 1992-93. The total ozone amount was 2 to 3% lower than in any earlier year...The Southern Hemisphere "ozone hole" increased in 1992 to an unprecedented 27x106 km2 in size, and depletion rates were faster than ever before recorded."
But the effect was only temporary. Even relatively small scale eruptions reduce global warming. A recent study suggested Moderate Volcanic activity slowing global warming by 25%.
Ken Caldeira from a September 2011 interview identified hydrological impacts from the Mount Pinatubo eruption, "the aerosols dropped out of the stratosphere within a year or two. After that in both the Amazon River and the Ganges there was very low river flow and droughts were experienced."
There has also been research from Japan which proposed the theory that atmospheric nuclear testing in the mid 20th century stagnated global temperatures. Regional limited nuclear war could also have a global cooling impact through injecting massive quantities of particles into the atmosphere driving down temperatures by about 1.5 degrees Celsius and a 10 per cent reduction in rainfall for up to 10 years.
Injection 5 times scale of Pinatubo required every year
Angus Ferraro, one of the study authors who now works at the University of Exeter, said: "To reduce global temperatures enough to counter effects of global warming would require a massive injection of aerosol - the small particles that reflect sunlight back into space. This would be equivalent to a volcanic eruption five times the size of that of Mount Pinatubo in 1991 every year."
Dr Andrew Charlton-Perez, University of Reading, one of the co-authors of the research, said in a media release:
"We have shown that one of the leading candidates for geo-engineering could cause a new unintended side-effect over a large part of the planet.
"The risks from this kind of geo-engineering are huge. A reduction in tropical rainfall of 30% would, for example, quickly dry out Indonesia so much that even the wettest years after a man-made intervention would be equal to drought conditions now. The ecosystems of the tropics are among the most fragile on Earth. We would see changes happening so quickly that there would be little time for people to adapt.
"Discussion of geo-engineering often prompts heated debate, but very often there is a lack of understanding of what putting large amounts of aerosol in the stratosphere will do to the complex climate system. Our findings should help to fill in some of the gaps about one of the leading candidates."
The study's conclusions states:
This letter has compared the impacts on the tropical temperature profile and overturning circulation of geoengineering with sulfate aerosol ('4CO2 + Sulfate') and solar dimming ('4CO2 + Solar'). Removing surface warming removes surface-mediated effects on precipitation, unmasking the fast radiative response of precipitation to CO2 increases in the '4CO2 + Solar' case (figure 4(c)), as suggested by Bony et al . Sulfate geoengineering, however, enhances the fast response of precipitation to CO2 increases.
When stratospheric aerosol geoengineering is represented more realistically using a sulfate aerosol layer there is additional atmospheric heating from the aerosol layer which weakens the tropical circulation, suppressing convection and further reducing precipitation. Consequently, though stratospheric aerosol geoengineering could be used compensate for the surface warming produced by CO2 globally, or even regionally, there is a tropical precipitation change of the opposite sign to and greater in magnitude than the long-term response to CO2. Climate model simulations representing geoengineering as solar dimming [16–18] do not represent this effect.
Such climatological precipitation changes are of considerable importance in regions vulnerable to droughts and floods, as well as being drivers of changes in agricultural production. Precipitation changes can be caused by changes in the atmospheric circulation as well as by direct radiative effect such as changes in evaporation rates. The results presented here highlight the importance of assessing the impacts of stratospheric aerosol geoengineering on large-scale circulation regimes, as well as on global-mean parameters, to appropriately characterize the effectiveness of such a climate intervention.
Using large scale geo-engineering in place of tackling the essential problem - the level of greenhouse gas emissions - may prove counterproductive and in fact worsen the climate crisis. It is all about risk management, and geo-engineering could so easily increase the level of risk.
Climate scientist Ken Caldeira from that September 2011 interview stated:
From an environmental point of view, you minimize risk by reducing interference in natural systems. So I think that not putting aerosols in the stratosphere is the least risky option. My basic feeling is that things would have to get pretty bad before you want to deploy a system like this because the potential risk of something going wrong is pretty high. And also politically, whoever decides to deploy such a system would have to take all of the political heat of getting blamed for every bit of bad weather on the planet. The other kind of issue is: who would deploy it? Let’s say crops were failing throughout the world and let’s say a country was threatened with massive famine and starvation and if its leader thought that deploying a system like this would save their population it would be hard to imagine that a politician could resist the pressure to do this. I would say that politicians would have to feel that they are pretty much backed up against the wall and see this as the only way out.
Study confirms previous research on aerosol impact on hydrological cycle
A study published in December 2013 also cast strong doubt on the efficacy of solar radiation management. The study argues different roles that solar and terrestrial radiation play in the surface energy balance and that the simultaneous changes in the water cycle and the atmosphere cannot be compensated for at the same time. Therefore, reflecting sunlight by geoengineering is unlikely to restore the planet’s original climate. A. Kleidon and M. Renner from the Max Planck Institute for Biogeochemistry argue in their study - A simple explanation for the sensitivity of the hydrologic cycle to surface temperature and solar radiation and its implications for global climate change (abstract) published in Earth System Dynamics that:
We illustrate an implication of this explanation for geoengineering, which aims to undo surface temperature differences by solar radiation management. Our results show that when such an intervention compensates surface warming, it cannot simultaneously compensate the changes in hydrologic cycling because of the differences in sensitivities for solar vs. greenhouse-induced surface warming. We conclude that the sensitivity of the hydrologic cycle to surface temperature can be understood and predicted with very simple physical considerations but this needs to reflect on the different roles that solar and terrestrial radiation play in forcing the hydrologic cycle.
The Reading University study confirms previous research by Kevin Trenbeth and Aiguo Dai which examined the impact of recent volcanic eruptions, particularly Mount Pinatubo, on the hydrological cycle. Their study - Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering - noted the reduction in rainfall and streamflow in the tropics and the widespread application of moderate or severe drought in many regions of the earth following the 1991 Pinatubo eruption.
During the 1992 water year, the precipitation is 3.12 standard deviations (0.069 Sv, computed with 1992 included) below normal and the river discharge is 3.67 standard deviations (0.031 Sv) below normal, both highly statistically significant at <1% level (and <0.1% level for the latter).
The corresponding regional changes in precipitation, runoff streamflow and river discharge are also correspondingly greater in the Tropics (Figures 3a and 3b), a point emphasized by plotting in units of mm/day, while higher latitude effects are better illustrated by the Palmer Drought Severity Index (Figure 3c); a normalized drought index reflecting the balance between atmospheric moisture supply (i.e., precipitation) and demand based on a crude estimate of evapotranspiration (a function of temperature) [Dai et al., 2004]. Widespread regions of moderate or severe drought occurred following the Pinatubo eruption, and the year 1992 has a peak percentage of global land areas under drought conditions [Dai et al., 2004].
Trenbeth and Dai conclude in their 2007 paper, "Creating a risk of widespread drought and reduced freshwater resources for the world to cut down on global warming does not seem like an appropriate fix. Our results suggest that considerable caution should be used regarding any intentional human intervention in the climate system that we do not fully understand."
Aerosol sulfate injection ignores Ocean acidification problem
As Trenbeth and Dai state, "Geoengineering by blocking the sun addresses neither the central problem of climate change nor acidification of the oceans."
Geo-engineering projects do little to change the crisis of uptake of CO2 in our oceans - ocean acidification - which is proceeding at an unprecedented rate not seen in the last 300 million years. We know that Anthropogenic climate change is driving Ocean Acidification threatening marine ecosystems.
Due to multiple human impacts, Oceans are at high risk of unprecedented Marine extinction scientists warn. In geo-engineering circles, ameliorating the CO2 uptake in the ocean sink - ocean acidification - is largely ignored, but it is a very real issue which only reducing our greenhouse gas emissions will address.
Professor Clive Hamilton, Professor of Public Ethics at the Centre for Applied Philosophy and Public Ethics and the Vice-Chancellor's Chair in Public Ethics at Charles Sturt University, raises serious issues with geo-engineering in this June 2013 youtube Video from Democracy Now. At 19:45 Hamilton talks about the possibility of aerosol injection disrupting the Indian monsoon and the geo-political consequences.
So we come back to the necessity for removing the essential cause of climate change, our excessive greenhouse gas emissions. Co-author of the paper Professor Ellie Highwood, University of Reading, said:
"Climate scientists agree that cutting carbon emissions is still necessary to curb the damaging effects of future climate change. However, since such cuts are far from certain to materialise, proponents of geo-engineering research argue that whatever the world decides on its carbon emissions, it would be prudent to explore alternatives that might help us in the decades ahead.
"On the evidence of this research, stratospheric aerosol geo-engineering is not providing world leaders with any easy answers to the problem of climate change."
While Climate engineering research is vital to prevent misinformation and poor decision making, implementation of geo-engineering schemes carries substantial risks to human populations and earth ecosystems. We are already geo-engineering the earth with our carbon emissions. The easiest place to start is to reverse that emissions trend rapidly to near zero.
- Angus J Ferraro et al 2014 Environ. Res. Lett. 9 014001, Weakened tropical circulation and reduced precipitation in response to geoengineering (Full paper) doi:10.1088/1748-9326/9/1/014001
- University of Reading media release, 8 January 2014 - Artificially cooling planet would cause climate chaos, scientists say
- Image of Global average temperature change between 1950- 2008 showing major volcanic activity and ENSO - University of Arizona, May 2009 - A warming world interspersed with cooling periods
- Stephen Self, Jing-Xia Zhao, Rick E. Holasek, Ronnie C. Torres, and Alan J. King, The Atmospheric Impact of the 1991 Mount Pinatubo Eruption, USGS. Retrieved 10 January 2014.
- Trenbeth and Dai (2007), Geophysical Research Letters - Effects of Mount Pinatubo volcanic eruption on the hydrological cycle (PDF)
- Interview with Ken Caldeira, September 2011, The European - The Atmosphere Should Not Be Our Waste Dump
- Kleidon, A. and Renner, M.:A simple explanation for the sensitivity of the hydrologic cycle to surface temperature and solar radiation and its implications for global climate change (abstract - Full paper available), Earth Syst. Dynam., 4, 455-465, doi:10.5194/esd-4-455-2013, 2013.
- European Geosciences Union media release 5 December 2013 - Press Release: Geoengineering approaches to reduce climate change unlikely to succeed