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Wullie Davidson: June until August, 2023 – Climate Events

Global Temperature Anomaly

Globally, the June to August period was the warmest in a record going back to 1860, at 1.17 C warmer than the 1951-80 average. This beat the previous record of +0.94 C set in 2022. June beat its record by 0.16 C, July by 0.25 C and August by 0.22 C.

NASA/GISS Global Land-Ocean Temperature Anomaly. Base Period 1951-1980.

These are very large margins, and scientists don’t really know what’s causing it. Record breaking global sea surface temperatures (SSTs) were first seen in March and continue unabated, also exceeding previous records by huge margins. It therefore seems very likely that the primary driver for the record global temperatures is the heat coming from the ocean, and some have pointed the finger at the El Nino in the Pacific. However, although the El Nino is currently strong, at 1.6 C above normal, the high global SST anomalies preceded its onset. Moreover, the very strong 2015-16 El Nino, which exceeded 2 C above normal, caused only modest record SSTs, compared to what we’re seeing today. Something else must be going on, but no one’s quite sure what.

Global Daily 2 Metre Air Temperature 1979-2023

Global Daily Sea Surface Temperature (SST) 1981-2023

Scientists acknowledge that global warming will not be a purely linear process. It is likely to accelerate as it progresses, and this trend may be punctuated by ‘step changes’, when there is a sudden lurch into a new regime when ‘tipping points’ are reached. Analysis of Greenland ice cores reveals local temperature changes of 10 C in as little as a decade at the end of the last Ice Age.

Antartic Sea Ice

Antarctic sea ice reaches its maximum extent at this time of year, but the current maximum is a record low, again by a large margin. This may be an example of a step change, but it’s only a few years since the ice was at a record high for the date, so it may not be sustained. Positive feedback effects may contribute to these step changes. It’s possible that the very recent large increase in global SSTs might be caused by the onset of a little heard of positive feedback, called ‘ocean surface stratification’. The ocean absorbs about 90% of the heat trapped by greenhouse gases. The water at the surface mixes with deeper water, transporting the heat energy to the depths. However, some scientists believe that, as SSTs increase, the surface water will not mix as easily with deeper water, so more of its energy will be released to the atmosphere. It’s a plausible mechanism to explain the warming, but there is no consensus among scientists on the subject.

US Billion Dollar Disasters

With more than three months of 2023 still left, the US has set a new record for the most natural disasters that have cost a billion dollars or more. Fires, floods and winds are among the deadly events that scientists believe are being exacerbated by climate change. The NOAA announced that there have already been 23 extreme weather events that have cost at least $1 billion. This surpasses the 22 events in 2020. The Hawaii wildfires that killed 95 people on Maui, making them the most deadly wildfires in the US for over 100 years, caused damages in excess of $5.5 billion. The Atlantic hurricane season has been more active than usual, but few storms have threatened land. Hurricane Idalia caused more than $1 billion in damages in the US, despite making landfall in a sparsely populated area

Storm Daniel and Medicanes

[[File:Daniel 2023-09-09 1200Z.jpg|Daniel 2023-09-09 1200Z]]

Currently, more than 11,000 people are believed to have been killed by storm Daniel in Libya, with around 10,000 people still missing. Daniel was a Mediterranean tropical-like cyclone, also known as a ‘medicane’. There are usually one or two of them in the Mediterranean each year, but they were only identified by satellite monitoring in the 80s. Prior to Daniel, the deadliest medicane known killed almost 600 people in 1969, left 250,000 homeless, and severely damaged local economies. A 20,000 ton tanker split in two off Malta, and phosphate mines in Tunisia were flooded, putting 25,000 out of work.

Tropical cyclones usually form over areas of the ocean that have SSTs of 26 C or higher, but can sometimes form over cooler waters if the air in the upper atmosphere is colder than normal, as this enhances convection. For medicanes, cold air aloft is a much more important factor in their development. In early September, the jet stream plunged south into the Mediterranean, bringing cold air. It then formed an ‘omega block’, so called because it takes the shape of the Greek letter, omega (Ω), over western Europe and the UK, dragging hot air north from north Africa. This gave the UK its warmest day of the year (32.7 C), and a record six consecutive days over 30 C in September. The high, cold air it brought to the Mediterranean, together with SSTs 2 C higher than normal, resulted in the formation of Daniel. The warming of the Mediterranean, combined with the jet stream now plunging further south than in the past, due to Arctic warming, could mean an increase in medicanes in the future.

Tiger Mosquitoes in Paris

https://upload.wikimedia.org/wikipedia/commons/b/b6/CDC-Gathany-Aedes-albopictus-1.jpg

As the world warms, mosquitoes and the diseases they carry will spread outwards and upwards into regions where the populations are immunilogically naive . Disease outbreaks in these new areas are therefore likely to be worse than they are in endemic areas.

The tiger mosquito has spread from its native south east Asia, and first appeared in southern Europe about 20 years ago. It has since spread further north, including into Germany, and is becoming increasingly common throughout Europe. Health experts say that it has thrived on the continent, in part, because of climate change. Warmer weather shortens the incubation period for its eggs, while warmer winters are no longer cold enough to kill it off. The diseases that it carries include Dengue fever, Chikungunya and Zika. It has now spread to Paris, and in August the Parisian health authorities fumigated an area of the city to control it. The area was a 150 metre circle around the home of a person who had contracted Dengue fever while travelling. If a tiger mosquito bites someone with the disease, it may become a carrier of the disease, potentially infecting others. The health authority may have acted from an abundance of caution, but it may only be a matter of time before mosquito borne diseases become endemic in Europe.

Wullie Davidson, September, 2023

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