Hurricanes & Tropical Cyclones: The Link to Climate Change

Dr. Jeff Obbard*

*Jeff is a Professor of Environmental Science, currently based at Qatar University. He was previously based at the National University of Singapore, where he served as Director for the Sustainable Development & Water Alliance, and Research Director for the Tropical Marine Science Institute. He has been identified in Singapore as a Top 100 Global Sustainability Leader, and is a recipient of the United Nations Mondialogo Award on sustainable development. Jeff was an invited Expert Reviewer for the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report.

September 2017

The devastation of Hurricanes Irma and Maria in the Caribbean in September has prompted questions as to whether the ferocity of these tropical storms was linked to climate change. Whilst impossible to attribute a single weather event to our changing climate, scientific climate observations clearly show that hurricanes and cyclones are set to become more intense and frequent, with concomitant risks for life and property.

Hurricane Irma was both powerful (reaching Category 5) and large (bigger than France), and wreaked havoc across the Caribbean and Florida – killing 82 people in its wake. Irma, the most destructive Atlantic hurricane to strike the United States since Katrina in 2005, reached its peak intensity on 6 September with 185 mph winds. It followed hot on the heels of Hurricane Harvey in August, which dumped record levels of rain on Texas (over 100cm in 4 days) which caused widespread flooding and the displacement of 30,000 people. Irma was shortly followed by Hurricane Maria, initially a Category 5 storm – yet another shot across the bows of the Caribbean. Does this season’s hurricane season have the fingerprints of climate change on it?

The term ‘dangerous anthropogenic climate change’ was first used at the United Nations Framework Convention on Climate Change (UNFCCC) in 1992, when the international community agreed to reduce atmospheric concentrations of greenhouse gases (GHG) with the goal of “preventing dangerous anthropogenic (human) interference with Earth’s climate system”¹.  Since then global carbon emissions have increased by almost 50%, and the size of the world’s economy has doubled². In its latest climate assessment (AR5) the Intergovernmental Panel on Climate Change (IPCC) made clear and  unambiguous statements about the status of climate change i.e.: i) warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia; ii) atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years, and; iii) it is extremely likely (95-100% probability) that human influence was the dominant cause of global warming between 1951-2010³.

‘Dangerous climate change has now become synonymous with a ‘policy guiderail’ of limiting the rise in average global mean surface temperatures (AGMST) as a result of human GHG emissions to no more than 2^oC above a pre-industrial baseline. This guiderail has become ingrained in climate change policy via a series of UN conferences of the parties (COP) under the UNFCCC framework, culminating in the 2015 Paris Climate Agreement (PCA) which states, as a long-term goal, keeping the increase in AMGST to well below 2°C above pre-industrial levels, with the aim to limit the increase to 1.5°C⁴.

Although the PCA is commendable, at least from the diplomatic perspective, there is growing concern that the 2^oC guiderail is based more on political expediency than scientific accuracy. Certainly, when evaluated in the context of contemporary ‘real-world’ observational changes in the global climate system, and evidence from the Earth’s climate history (or paleoclimate) record, then the 2oC is overly generous and misguided. Analyses of global climate data for the year 2016 by the World Meteorological Organization⁵, show that AMGST were the highest since instrumental temperature records began in 1880. Temperatures were an average of 1.1^oC warmer in 2016 than the mid-20th century mean, with several months in 2016 reaching almost 1.5^oC above pre-industrial levels. Indeed, 2016 was the third year in a row to set a new record high for AMGST temperatures, where 16 out of the first 17 years of the 21st century have all exceeded pre-industrial temperature records. More recently, leading climate scientist Dr. James Hansen, has highlighted the risk of extreme summer temperatures as a result of climate change, and concludes that AMGST for 2016 were 1.28^oC above average, with the warming trend continuing into 2017⁶.  In short, we are already flirting dangerously with the 1.5^oC goal of the PCA.

Hurricanes and tropical cyclones are complex phenomenon: both naturally occurring and notoriously difficult predict – even without the backdrop of rising global temperatures. A changing climate exacerbates the risk of an increased frequency and intensity of storm events, and makes them even more deadly. Higher sea levels, caused by the thermal expansion of the world’s oceans and melting glaciers/ice caps increase storm-surge levels; and higher sea temperatures add fuel to these weather systems which are born over the oceans, and from which they derive their energy. A warmer atmosphere also holds more moisture, where for every extra degree Celsius in warming the atmosphere holds 7% more water (Clausius–Clapeyron equation) which makes rainfall events more extreme. Recently, Hansen et al. (2016)⁷ highlighted the risk of ‘super-storms’ and accelerated sea level rise if current warming trends, ice-melt and changing atmospheric circulation patterns are allowed to continue. In this context, Hurricanes Harvey, Irma, and Maria are just precursors of the intensity of storms in the future – if climate change is not stopped.

The scientific evidence is clear – in the absence of concerted global GHG emission reductions the risk, frequency and impact of hurricanes and tropical cyclones will increase. Despite the PCA being a landmark achievement in the world’s attempt to avoid dangerous climate change there is still a glaring disparity between the scale of GHG emission reductions actually needed to stay within the 2^oC guiderail (let alone 1.5 ^oC) and those actually pledged under the agreement. Indeed, the International Energy Agency (IEA), has recently stated that current commitments (known as nationally determined contributions, or NDCs) will result a temperature increase of 2.7 ^oC by 2100, and above 3^oC thereafter⁷. This precarious scenario for future climate security has been further denigrated by the unilateral decision of the United States of America, the world’s second largest GHG emitter after China, to withdraw from the Paris Agreement in June 2017.

On a more positive note, despite the US withdrawal, a renewed international commitment to the goals of Paris Agreement was evident at the COP22 in Morocco in November 2016. Furthermore, COP 23, which will take place in Bonn this November, will place focus on the implementation of the PCA, and aims to galvanize international climate action, despite the US decision.  At a prelude to COP 23, during a September meeting in Montreal of global environment ministers China, Canada and the European Union boldly stated that the goals of the Paris Agreement are irreversible and non-negotiable. The European Union Commissioner for Climate Action and Energy, Miguel Arias Cañete, said that “In the case of collapse of ambitions by the United States, the European Union will make sure to make our planet great again.” This sentiment was echoed by China’s special representative for Climate Change Affairs, Mr. Xie Zhenzua, who said “We cannot let the Paris agreement fail.” For the sake of a cooler and more secure global climate for all, let’s hope massive, coordinated global action prevails.

References

1. United Nations (9 May 1992), United Nations Framework Convention on Climate Change, New York.

1. What Lies Beneath. The Understatement of Climate Risks.  Eds. Sprat D. and Dunlop I.

3. IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. R.K. Pachauri and L.A. Meyer (eds.). IPCC, Geneva, Switzerland.

1. Paris Agreement. United Nations Treaty Collection. https://treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-7-d&chapter=27&clang=_en, 8 July 2016.
2. World Meteorological Organization (January 2017).   WMO confirms 2016 as hottest year on record, about 1.1°C above pre-industrial era. https://public.wmo.int/en/media/press-release/wmo-confirms-2016-hottest-year-record-about-11%C2%B0c-above-pre-industrial-era.
3. Hansen J.  Global temperatures. See: http://www.columbia.edu/~mhs119/Temperature/
4. Hansen J. et al. (2016) Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 ◦C global warming could be dangerous.  Atmos. Chem. Phys., 16, 3761–3812.
5. Energy Technology Perspectives, 2016. International Energy Agency, https://www.iea.org/publications/freepublications/publication/EnergyTechnologyPerspectives2016_ExecutiveSummary_EnglishVersion.pdf.