Subtropical Storm Alberto
At the end of May there was an unusual event unfolding in the Western Caribbean. It was the formation of the first named storm of the 2018 hurricane season. The hurricane season is typically a period of the annual formation of tropical cyclones (low pressure systems). It runs from early June to late November. There have been four consecutive years where the storms have formed before the official start of the season. An area of low pressure first formed over the south west Caribbean Sea on May 21 but tracked north and west to become stronger. It was classified as Subtropical Storm Alberto on 25 May. The warm water of the Gulf of Mexico was a higher temperature than average which assisted the formation of a strengthening tropical storm. On the 30 May the storm had reached Lake Michigan with more power than in the Gulf. This is the unusual feature of Alberto.
The storm hit land in Florida and continued to track northwards all the way to Lake Huron. It was the first tropical depression to go to Lake Huron before June 1st since records began in 1851. See this Weather Network article. Alberto was a subtropical storm which has elements of warm air and colder air above, unlike tropical storms where the air above and below is warm. Unusually it was reclassified to become a tropical storm inland over Tennessee. It continued to be a tropical storm up to Lake Michigan. After this it was loosing power transitioning to become a post-tropical cyclone.
Normally the storm will typically be a subtropical storm over land as the air mixture changes from fully warm air to a mix of colder and warmer air. It appeared that Alberto was following this pattern with the cyclone weakening to become a subtropical depression shortly after landfall in Florida but later gained momentum and became tropical over Tennessee. The reason for this storm tracking further north could be down to something known as the “Brown Ocean Effect” where the land’s surface are similar to the sea (being a source of warm conditions at the ground level – as the sea would be – and in the air above).
Details of the 2018 Hurricane Season will be provided on this Wikipedia Page. Alberto starts off the 2018 season earlier than usual and in a most strange way.
Melting Antarctic Ice
Ice melt in the antarctic is accelerating. Over the last 25 years three trillion tonnes of ice have melted. Satellites monitoring Antarctica show that around 200 billion tonnes of ice a year are melting with the water going into the ocean. This large scale ice melt is having an impact on sea levels. They are increasing at a historically significant rate of around 0.6 millimetres per annum. Despite the increase sounding tiny, this is a threefold increase from just 6 years ago when a previous survey was undertaken.
A Nature report entitled “Mass Balance of the Antarctica Ice Sheet from 1992 to 2017” highlights the driver of sea level change and reviews the state of the ice sheet. The mass balance illustrates whether an ice sheet is growing (gaining ice), shrinking (losing ice) or remaining stable. Satellites have been used to determine the Antarctic Ice Sheet’s changing volume as it changes through ice melt and other processes. The study also reviewed flow and gravitational attraction with modelling of the ice surface mass balance. This highlighted that it had lost 2,720 ± 1,390 billion tonnes of ice over the period 1992 to 2017. This would correspond to an increase in mean sea level of 7.6 ± 3.9 millimetres. Ice loss from the ice sheet has increased from 53 ± 29 billion to 159 ± 26 billion tonnes per year from 1992-2017. Part of the reason for the increased loss of ice is the ice shelf collapse.
Ice sheets in Antarctica hold enough water to raise global sea levels by up to 58 metres. Floating ice sheets that have melted have been responsible for triggering inland ice flows and accelerating the movement of glaciers into the sea. This is an example of a positive feedback event whereby changes lead to further changes. In this case melting ice is accelerating other ice flows and drawdown which then lead to further faster melting of this source of ice.
A number of satellite monitoring techniques have been developed over the years to monitor the changes in the Antarctic Ice Sheet. These have been enhanced over the years and this study is providing an inter-comparison of 12 estimates that are based upon models. Methods combined studies for three geographical extents covering these ice sheets: East Antarctic Ice Sheet (EAIS), West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula Ice Sheet (APIS). Mass changes where calculated over common time frames. Cumulative changes were calculated to show that ice is being lost at an increased rate. There is a dominance of solid ice discharging into the ocean (see for example an article posted previously: Iceberg!).
Measuring the changes across the Antarctic present several challenges due to the size of the continent. There are now many reliable techniques that are improving that demonstrate the ice melt. This will have consequences for global sea levels and more than likely accelerate rising levels that may have been under estimated in previous studies. Information such as this will eventually feed into InterGovernmental Panel on Climate Change (IPCC) reports which give an idea of the state of the climate. The IPCC will soon be publishing a report on the impact of a 1.5 Celsius increase in temperature (see below).
IPPC Special Report Due In September
The InterGovernmental Panel on Climate Change (IPCC) is due to publish a special report in September 2018 on the impacts of 1.5 Celsius global warming above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) report will consider what would need to be done to limit global warming to 1.5 Celsius. The report has a rather long title “Global Warming of 1.5°C: an IPCC special report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty”.
The report will consider the following topics:
- Summary for Policy Makers
- Chapter 1: Framing and context
- Chapter 2: Mitigation pathways compatible with 1.5°C in the context of sustainable development
- Chapter 3: Impacts of 1.5°C global warming on natural and human systems
- Chapter 4: Strengthening and implementing the global response to the threat of climate change
- Chapter 5: Sustainable development, poverty eradication and reducing inequalities
This report follows on from the Paris Climate Conference in 2015 and will review the likely pathway of a global increase in temperatures of 1.5 degrees which is the likely scenario (although this may well be exceeded). The report will aim to strengthen the global response to the threat of climate change and will be in context of sustainable development and eradication of poverty.