Saturday, January 25, 2014

ExClimate: Week 3.3 - Extreme events and climate Discussion

This article is a little bit of a tangent to my regular articles. I am presently doing an online course - Climate Change: Challenges and solutions - offered by the University of Exeter (UK). So please indulge me as I also use this blog for some climate course work. This article is for section 3.3 of the course on State of the climate extreme events.

1. Climate event for 2012 - Cat 4 cyclone Evan in South Pacific devastates Samoa and Fiji

Select an extreme weather event from 2012 (list provided). Does this provide further evidence of climate change or does it add more complexity to the issue?

I chose severe Tropical Cyclone Evan, a category 4 storm which devastated Samoa and Fiji in December 2012. While this particular storm was primarily part of natural climate variability, it fits the trend for more intense tropical cyclones which climate models and climate physics tells us is likely to occur.

Tropical cyclones on a global level are forecast to stay at about the same frequency, but with a greater number of intense tropical cyclones/hurricanes/typhoons occurring, according to the 2011 IPCC SREX Summary for Policymakers report.

Two of the factors in a warming world that are contributing to more intense cyclones: warmer sea surface temperatures globally and around Australia are providing more energy for storm systems to feed from, and a warmer atmosphere increasing the moisture carrying capacity providing the opportunity for heavier torrential rainfall and flood events that can devastate communities, particularly in mountainous areas where landslides are more prevalent.

More intense cyclones also increase storm surge. On top of rising sea levels caused by climate change, storm surges can result in saltwater intrusion damaging freshwater supplies and staple crops. See (James P Terry et al 2010) - Responses of Atoll freshwater lenses to storm-surge overwash in the Northern Cook Islands from Hydrogeology Journal.

2. Will there be more rain or does it depend on where you are?

As the atmosphere warms it can hold more water, but is a warming world likely to have more rain, or does it depend on where on Earth you are?

It depends on where you are on earth. Rainfall patterns are likely to change as atmospheric and ocean circulation patterns change. For example, global warming is causing shifts in the rain band of the South Pacific Convergence Zone causing an increase in extreme weather across the island nation states of the South Pacific.

Generally, as a large scale tendency, wet areas are likely to get even wetter and dry areas are likely to get even drier. On a global level a trend has been detected for Increases in rainfall extremes linked to global warming (Westra et al 2013) See this article at the Conversation website: Increases in Rainfall extremes linked to global warming

This NOAA Geophysical Fluid Dynamics Laboratory Youtube video explains how the subtropics in both the Northern and Southern Hemisphere will have enhanced evaporation with the precipitation moving poleward to the sub-polar latitudes which will receive more precipitation.

Some regional long term precipitation and stream flow trends can already be seen in Australia. For example, the south west of Western Australia has a pronounced long term historical trend of less precipitation. South east Australia also has a long term trend of decreasing rainfall, although not as pronounced as WA.

El Niño Southern Oscillation is already showing signs of increasing intensity. El Niño intensification in the future is likely to lead to stronger droughts for Australia. Global warming may be doubling the risk of Extreme El Ninos.

Single weather events are much harder to attribute to climate change, although there is a whole area of recent research on Fractional attribution of risk of single weather events to statistically model the event to determine the statistical probability of or likelihood that it was influenced by climate forcings.

This was done for the 2000 Floods in England and Wales (Pall et al 2011), the 2003 European heatwave (Stott et al 2004), the 2010 Russian heatwave (Otto et al 2012) and Australia's record year of temperatures in 2013. While many extreme weather events are still within natural climate variability, increasingly we will see more that are clearly part of a new normal, especially as cities pass their climate departure point.

Dim Coumou & Stefan Rahmstorf in their March 2012 paper - A decade of weather extremes - say in the abstract:

The ostensibly large number of recent extreme weather events has triggered intensive discussions, both in- and outside the scientific community, on whether they are related to global warming. Here, we review the evidence and argue that for some types of extreme — notably heatwaves, but also precipitation extremes — there is now strong evidence linking specific events or an increase in their numbers to the human influence on climate. For other types of extreme, such as storms, the available evidence is less conclusive, but based on observed trends and basic physical concepts it is nevertheless plausible to expect an increase.

3. Record High Antarctic sea ice

While Arctic sea ice fell to new lows, Record high Antarctic sea ice produced a paradox which a number of scientific studies have tried to address. The destruction of the ozone hole above Antarctica has had a cooling effect which has intensified the Westerlies around the continent and Katabaric winds off the continental plateau. Several studies identify that the increased wind blows the sea ice north away from the continent creating space for the formation of new sea ice. one of the more recent papers arguing this is by (Zhang 2013), from the University of Washington. He argues that about 80 percent of the growth can be explained by changes in the prevailing winds around the frozen continent - the westerlies; the remaining 20 percent, he suspects, might be the result of changes in ocean circulation.

However a Dutch study (Bintanja et al 2013) suggested that freshly melted cool and fresh water forms a surface layer protecting sea ice and helping it's expansion insulating it from the deeper warm salty currents. Antarctica, especially in the Amundsen sea area of West Anarctica and the Antarctic peninsular is losing ice mass at an accelerated rate, this includes from the maasive Pine Island Glacier.

It is likely that strengthening of circumpolar winds, the westerlies have played a major role, but perhaps there is also a role for new melt water from the West Antarctic Ice Sheet is producing an insulation layer improving sea ice formation. The scientific studies indicate likely theories, but the science in this area is not settled. Changes in the Antarctic regional climate are being actively studied. Slow record growth in winter Antarctic sea ice reveals the counter intuitive complexity and a paradox of global warming.

Read more from my previous articles on this issue:


3.5 Urgent Action

Observations: air temperatures, sea level and reductions in Arctic sea-ice. The statement also refers to sea temperatures, atmospheric water vapor, mountain glacier retreat, snow cover reduction, and melting permafrost.

I live in an urban environment with an increasing frequency and intensity of heatwaves amplified by the urban heat island effect. So extremes temperatures are a primary public health concern.

There was also Stressed electricity Infrastructure during the heatwave.

Rising temperatures also dry out vegetation and soil moisture increasing fire weather conditions for bushfire. The 2009 Black Saturday bushfires directly killed 173 people, but 374 likely died from heat related causes, mainly elderly people.

During last week's Australian heatwave, the Victorian Ambulance Service reported 700 per cent rise in number of call-outs for cardiac arrests when temperatures spiked at almost 44C; 203 deaths were reported to the coroner, more than twice the average; paramedics treated >500 people for heat exhaustion, 60 kids were found locked in cars. See ABC Report

Heatwaves can also occur during winter impacting Winter Chill on certain orchard crops affecting agricultural productivity.


3.7 Global carbon emissions

The World Bank publishes a variety of environmental data, including carbon emissions (measured in kt). Create a graph to show a variety of countries at different levels of economic development by following this link to the World Bank web site. Include the USA and China in your graph. Share your graph in the discussion. You may also want to try plot carbon dioxide emissions measured in metric tons per capita. What conclusions can you draw?

CO2 Emissions (kt) for China, United States, Australia, Fiji, India, Japan, Canada:

Data from World Bank

CO2 emissions per metric tons per capita for China, United States, Australia, Fiji, India, Japan, Canada:

Data from World Bank

While Australia's emissions as a proportion of total global emissions are relatively low, on a per capita basis they rank along with the USA. Although China's total emissions have increased markedly to exceed emissions from the USA, on a per capita basis they are a third of the emissions of Australia or USA. India is also increasing as a proportion of global emissions, but on a per capita basis still ranks near the bottom.

Developed nations, for the last 150 years, have been the primary cause of increased carbon dioxide and other greenhouse gas emissions in the atmosphere. They have a substantial carbon debt to developing countries on a per capita basis. If we are to reduce carbon emissions,developed countries need to make rapid reductions in emissions and also assist with technology transfer to assist developing countries to develop in carbon free and sustainable ways.

We are starting to see more action on carbon reduction. China is roaring ahead with Renewables while President Obama has set out a climate action plan of regulatory action. Australia seems intent in undoing climate action with a new conservative Government elected in September 2013. At the climate negotiations in Warsaw Australia won an unprecedented fourth Fossil of the Day award for finance stance. Japan's reduced emissions targets were also a setback to COP19 climate change negotiations.

The atmosphere is the commons which every person and country has the same right to. Any global agreement must recognise the historical responsibility for the problem of carbon pollution and address this with their emissions reduction targets. That is the essence of climate justice.