Potential acceleration in global warming

Introduction

This article expands on material from a recent post by highlighting some subsequent news. For completeness, some of that recent material has been included again.

Global warming continues

Michael Mann is Distinguished Professor of Meteorology at Pennsylvania State University. In March last year, he commented on what had become known as “the pause” of recent times in global warming. He suggested that the term was a misnomer, as “temperatures still rose, just not as fast as during the prior decade”.

In the relevant article he went on to predict that we will reach 2 degrees Celsius temperature increase by around 2036. [1] It is difficult to overstate the seriousness of such an outcome, should it occur. 

Two months earlier, the Skeptical Science website (which uses the word “skeptical” in its true sense and takes climate change very seriously) reported that, in 2013, the equivalent of 12 Hiroshima atomic bombs of heat had been added to the oceans every second (up from an average of around 4 per second in the previous 16 or so years). [2] The accumulated number since 1998 is now over 2.2 billion. Based on those staggering numbers, it should be no surprise that we have a problem. The article also indicated that the oceans have been absorbing around 93% of the energy from global warming over recent decades.

It may be about to accelerate

Citing a study published in the journal Nature by Smith, et al., [3], climate change commentator Joseph Romm has indicated that the only pause “was in the long-expected acceleration of warming. That is, while the rate of global warming has been roughly constant for the last few decades, it should have started to speed up.” He went on to say that multiple studies, including this latest one, indicate that “we should expect a speed up very soon.” [4]

The authors of the Nature study modeled potential per-decade rates of temperature change over 40-year periods in respect of two RCPs (Representative Concentration Pathways) utilised by the IPCC (Intergovernmental Panel on Climate Change).

RCPs outline the trajectory of atmospheric greenhouse gas concentrations through to the year 2100 under different scenarios. Each is identified by a number representing its anticipated radiative forcing, which is a measure (in watts per square metre) of the balance of incoming and outgoing energy in the Earth-atmosphere system (including solar radiation and resultant infrared radiation that escapes to space or becomes trapped by greenhouse gases). The four pathways are: RCP2.6; RCP4.5, RCP6 and RCP8.5. (RCP2.6 is also known as RCP3-PD, with PD standing for “peak and decline”, whereby radiative forcing peaks at 3 watts per square metre and then declines to 2.6 before 2100.)

The various scenarios take into account greenhouse gas emissions, developments in technology, changes in energy generation, changes in land use, economic circumstances and population growth.

The RCPs utilised in the Nature study were RCP4.5 and RCP8.5. The former is regarded as a stabilisation scenario, where action is taken to limit greenhouse gas concentrations. RCP8.5 involves higher greenhouse gas emissions than under RCP4.5, that are still rising in 2100.

The results are shown in Figure 1. Even under the relatively conservative RCP4.5, the rate of change per decade had jumped from 0.07°C in 1990 to 0.21°C in 2010, and was anticipated to range from 0.25°C and 0.27°C between 2020 and 2050. [5] That implies a temperature increase of around 1°C over the coming forty years, in excess of the 0.85°C increase that has already occurred since pre-industrial times (which is slightly more conservative than Michael Mann’s estimate).

Under RCP8.5, per decade increases of just under 0.4°C would be occurring by 2050 (and higher figures subsequently), resulting in even more onerous outcomes.

Figure 1: 40-year global rates of temperature change (per-decade)

Some impacts of a 2°C temperature increase

Climate change author, Mark Lynas, has indicated some potential impacts of a 2°C temperature increase. [6]

European summers could generally be expected to be as hot as 2003, when 30,000 people died from heatstroke.

The Mediterranean area can expect six more weeks of heatwave conditions each year, with wildfire risk also growing, while its southern region would lose a fifth of its rainfall, with major implications for the tourism industry.

In Peru, the glaciers would disappear from the Andean peaks that currently supply Lima with water.

In California, the loss of snowpack from the Sierra Nevada,  three-quarters of which could disappear, would significantly affect the water supply of Los Angeles and other cities.

Global food supplies, especially in the tropics, would also be affected

A third of all species alive today may be driven to extinction as climate change destroys their habitat.

The temperature increase may be understated

As I have mentioned elsewhere, the models used by the IPCC do not allow for potentially critical “slow feedback” mechanisms, such as ice sheet growth and decay, changes in vegetation cover, and permafrost melting. By the time a temperature increase approaching 2°C has been reached, key climate change tipping points may have been breached, creating a very real risk of even higher temperatures and runaway climate change over which we will have little or no control. [7]

The Catch-22 of global warming

Our efforts to avoid accelerated warming are limited by the fact that we have created a possible “Catch-22” in the form of aerosols generated by the burning of fossil fuels. [Footnote 1] Aerosols are airborne particulates such as sulphates, nitrates, and dust from smoke and manufacturing. They have a cooling effect, sometimes referred to as “global dimming”, which has offset some of the warming effects of greenhouse gases. They only remain in the atmosphere for around ten days, so their cooling impact will be short-lived in any transition away from fossil fuels to less carbon-intensive energy sources.

The charts in Figure 1 include a range for uncertainties in aerosol forcing (grey shading).

It could be crunch time for Arctic sea ice

Current indications are that the winter maximum area of Arctic sea ice this year will represent a record low since satellite records began in 1979. [8] That might be an ominous sign in the context of an earlier prediction by Professor Peter Wadhams of Cambridge University, that the Arctic may effectively be free of summer sea ice (less than 1 million square kilometres) in September this year or next, with extremely serious flow-on effects. [9]

Conclusion

I trust that these comments add some context to discussions on the subject of climate change. I believe the more we understand the problem, the better placed we will be to contribute towards the urgent action that is required. [10]

Update

Additional information regarding the IPCC’s RCP scenarios added on 17th March, 2015, and reference numbers amended accordingly, along with other minor changes.

Author

Paul Mahony (also on Twitter, Scribd, Slideshare and Viva la Vegan)

Footnote

The term “Catch-22” originated in the 1961 book of the same name by Joseph Heller. The Oxford dictionary defines the term as “a dilemma or difficult circumstance from which there is no escape because of mutually conflicting or dependent conditions“.

References

[1] Mann, M.E. “Earth Will Cross the Climate Danger Threshold by 2036“, Scientific American, 18th March, 2014, http://www.scientificamerican.com/article/earth-will-cross-the-climate-danger-threshold-by-2036/

[2] Painting, R., “The oceans warmed up sharply in 2013: We’re going to need a bigger graph”, 31st January, 2014, http://www.skepticalscience.com/The-Oceans-Warmed-up-Sharply-in-2013-We-are-Going-to-Need-a-Bigger-Graph.html

[3] Smith, S., Edmonds, J., Hartin, C.A., Mundra, A., Calvin, K., “Near-term acceleration in the rate of temperature change”, Nature Climate Change, 9th March, 2015, http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2552.html

[4] Romm, J., “Rate of climate change to soar by 2020s, with Arctic warming 1°F per decade”, Climate Progress, 10th March, 2015, http://thinkprogress.org/climate/2015/03/10/3631632/climate-change-rate/

[5] Smith, et al. op cit., Supplementary Information,, Table SI-4, http://0-www.nature.com.es.library.du.ac.bd/nclimate/journal/vaop/ncurrent/full/nclimate2552.html#supplementary-information

[6] Lynas, M., “Six steps to hell”, The Guardian, 23rd April 2007, http://www.theguardian.com/books/2007/apr/23/scienceandnature.climatechange

[7] Spratt, D. and Dunlop, I., “Dangerous Climate Warming: Myth, reality and risk management”, Oct 2014, p. 5, http://www.climatecodered.org/p/myth-and-reality.html

[8] Thompson, A., “Arctic Sea Ice Dwindling Toward Record Winter Low“, Climate Central, 11th March, 2015, https://www.climatecentral.org/news/arctic-sea-ice-record-winter-low-18764

[9] Vidal, J. “Arctic expert predicts final collapse of sea ice within four years”, The Guardian, 17th September, 2012, http://www.theguardian.com/environment/2012/sep/17/arctic-collapse-sea-ice

[10] Mahony, P., “Climate Action”, 9th March, 2015, https://terrastendo.net/2015/03/09/climate-action/

Images

Main image: Global warming © Gorshkov13 | Dreamstime.com

Figure 1 image: Smith, et al. op cit., Figure 4, p.3. (Used with permission.)