No time to lose

Photo: Clive Simpson

POLITICAL hot air was a major feature across the world in 2016 as governments and electorates began to shift significantly on their axis of travel - now confirmation has come that it was also a year of record breaking global temperatures, exceptionally low sea ice and unabated sea level rise and ocean heat.

Issuing its annual statement on the State of the Global Climate ahead of World Meteorological Day today (21 March), the World Meteorological Organization (WMO) said extreme weather and climate conditions have continued into 2017.

Its report, based on multiple international datasets maintained independently by global climate analysis centres and information submitted by dozens of WMO and research institutes, is regarded as an authoritative source of reference.

Because the social and economic impacts of climate change have become so important, WMO partnered with other United Nations organisations for the first time to include information on these impacts.

“This report confirms that the year 2016 was the warmest on record – a remarkable 1.1C above the pre-industrial period and 0.06C above the previous record set in 2015. This increase in global temperature is consistent with other changes occurring in the climate system,” said WMO secretary-general Petteri Taalas.

“Globally averaged sea surface temperatures were also the warmest on record, global sea levels continued to rise and Arctic sea-ice extent was well below average for most of the year,” he added..

“With levels of carbon dioxide in the atmosphere consistently breaking new records, the influence of human activities on the climate system has become more and more evident,” said Mr Taalas.

The increased power of computing tools and the availability of long term climate data have made it possible today, through attribution studies, to demonstrate clearly the existence of links between man-made climate change and many cases of high impact extreme events in particular heatwaves.

Each of the 16 years since 2001 has been at least 0.4C above the long-term average for the 1961-1990 base period, used by WMO as a reference for climate change monitoring. Global temperatures continue to be consistent with a warming trend of 0.1 C to 0.2C per decade, according to the WMO report.

The powerful 2015/2016 El Niño event boosted warming in 2016, on top of  long-term climate change caused by greenhouse gas emissions. Temperatures in strong El Niño years, such as 1973, 1983 and 1998, are typically 0.1 C to 0.2C warmer than background levels, and 2016’s temperatures are consistent with that pattern.

Global sea levels rose very strongly during the El Niño event, with the early 2016 values reaching new record highs.  Global sea ice extent dropped more than 4 million square kilometres below average in November, an unprecedented anomaly for that month.

The very warm ocean temperatures contributed to significant coral bleaching and mortality was reported in many tropical waters, with important impacts on marine food chains, ecosystems and fisheries.

Carbon dioxide levels in the atmosphere reached the symbolic benchmark of 400 parts per millions in 2015 – the latest year for which WMO global figures are available – and will not fall below that level for many generations to come because of the long-lasting nature of CO2.

Among some of the most extreme events in 2016 were severe droughts that brought food insecurity to millions in southern and eastern Africa and Central America. Hurricane Matthew caused widespread suffering in Haiti as the first category four storm to make landfall since 1963, and inflicted significant economic losses in the United States of America, while heavy rains and floods affected eastern and southern Asia.

Newly released studies, which are not included in WMO’s report, indicate that ocean heat content may have increased even more than previously reported.  Provisional data also indicates that there has been no easing in the rate of increase in atmospheric carbon dioxide concentrations.

“Even without a strong El Niño in 2017, we are seeing other remarkable changes across the planet that are challenging the limits of our understanding of the climate system. We are now in truly uncharted territory,” said World Climate Research Programme director David Carlson.  

At least three times so far this winter, the Arctic has witnessed the Polar equivalent of a heatwave, with powerful Atlantic storms driving an influx of warm, moist air. This meant that at the height of the Arctic winter and the sea ice refreezing period, there were days which were actually close to melting point. Antarctic sea ice has also been at a record low, in contrast to the trend in recent years.

Scientific research indicates that changes in the Arctic and melting sea ice is leading to a shift in wider oceanic and atmospheric circulation patterns. This is affecting weather in other parts of the world because of waves in the jet stream – the fast moving band of air which helps regulate temperatures. 

Thus, some areas, including Canada and much of the USA, were unusually balmy, whilst others, including parts of the Arabian peninsula and North Africa, were unusually cold in early 2017.

In the USA alone, 11,743 warm temperature records were broken or tied in February, according to the US National Oceanic and Atmospheric Administration. Prolonged and extreme heat in January and February  affected New South Wales, southern Queensland, South Australia and northern Victoria, and saw many new temperature records.

Andrew Challinor, Professor of Climate Impacts at the University of Leeds, said: “The trend in extremes continues – as anyone shopping for salads and veg earlier this year will know. This new evidence comes just days after parliament discussed the independent report they commissioned on the implications of climate change for UK food security.

“Current government strategy emphasises the ability of markets to even out price fluctuations and ensure food supply. The independent report emphasises the need for more joined up thinking across governments and internationally.”

Prof Sir Robert Watson, Director of Strategic Development at the Tyndall Centre for Climate Change Research, University of East Anglia, said: “While the data show an ever increasing impact of human activities on the climate system, the Trump Administration and senior Republicans in Congress continue to bury their heads in the sand and state that climate change is a hoax and does not need to be addressed. We are now living in an evidence-free world, where facts are irrelevant.

“Our children and grandchildren will look back on the climate deniers and ask how they could have sacrificed the planet for the sake of cheap fossil fuel energy when the cost of inaction exceeds the cost of a transition to a low-carbon economy.

“How much more evidence does the world need to recognise the dangers confronting our society? The pledges of the Paris agreement are inadequate to limit human-induced climate change to 2C and need to be strengthened significantly – there is no time to lose.”

Arctic melt

New research has proposed a critical connection between sharp declines in Arctic sea ice and changes in the atmosphere - not only affecting ice melt in Greenland but also weather patterns all over the North Atlantic.

The studies centre on an atmospheric phenomenon known as ‘blocking’ - when high pressure systems remain stationary in one place for long periods of time (days or even weeks), causing weather conditions to stay relatively stable for as long as the block remains in place.

These can occur when there’s a change or disturbance in the jet stream, causing the flow of air in the atmosphere to form a kind of eddy, according to Jennifer Francis, a research professor and climate expert at Rutgers University.

Blocking events over Greenland are particularly interesting to climate scientists because of their potential to drive temperatures up and increase melting on the ice sheet.

“When they do happen, and they kind of set up in just the right spot, they bring a lot of warm, moist air from the North Atlantic up over Greenland, and that helps contribute to increased cloudiness and warming of the surface,” says Francis. “When that happens, especially in the summer, we tend to see these melt events occur.”

Two recent studies have suggested that there’s been a recent increase in the frequency of melt-triggering blocking events over Greenland - and that it’s likely been fueled by climate change-driven losses of Arctic sea ice.

A paper set to be published tomorrow (9 May 2016) in the ‘International Journal of Climatology’ reveals an increase in the frequency of these blocking events over Greenland since the 1980s.

A team of researchers led by the University of Sheffield’s Edward Hanna used a global meteorological dataset relying on historical records to measure the frequency and strength of high pressure systems over Greenland back to the year 1851. Previous analyses had only extended the record back to 1948, so the new study is able to place recent blocking events in a much larger historical context.

When the researchers analysed the data, they found that the increase in blocking frequency over the past 30 years is particularly pronounced in the summer, the time of year when blocking events are likely to have the biggest impact on ice melt.

What’s been causing this is a big source of interest for climate scientists hoping to gain a better understanding of the events affecting the vulnerable Greenland ice sheet.

In the new paper, Hanna and his colleagues suggested that declines in Arctic sea ice might be playing a role  -  and it’s a theory that’s heavily supported by another paper just out in the ‘Journal of Climate’. That study used both observational data and computer simulations to investigate the connection between sea ice declines and atmospheric changes in the Arctic.

Diminishing Arctic sea ice driven by climate change-induced warming is a well-established trend. Im April scientists reported that the maximum extent of Arctic sea ice over lastwinter had reached a record low for the second year in succession.

Interestingly, what happens on the surface of the ocean also has the potential to seriously influence activity in the atmosphere, adds Francis, a co-author on the study.

“When there’s less sea ice, obviously it’s a much darker surface that’s exposed to the sun - and especially in the late spring, early summer when the sun is really strong, that open water that would normally have ice on it absorbs a lot more of the sun’s heat.”

As a result, the surface of the ocean warms up and that extra heat is also transferred into the atmosphere. When this happens, lower layers of the atmosphere warm and expand, pushing up on higher layers of the atmosphere and causing the jetstream to bulge, as a result of the physics behind airflow in the atmosphere.

Since warm air takes up more space than cooler air, and the equator is the warmest part of Earth, the atmosphere is generally thickest there. This creates a kind of downhill ‘slope’ from the equator to the poles over which air flows.

Because the Earth is spinning so quickly, however, airflow ends up being pushed toward the east. The result is the jetstream - a current of air that generally flows from west to east around the world but also tends to meander north and south in wavy lines as it goes along.

If the Arctic warms more quickly than the rest of Earth, however, the downhill slope between the equator and the poles becomes less steep and this can weaken the jetstream’s flow, making it more susceptible to twists and turns.

So, as sea ice disappears and the atmosphere in the Arctic warms and expands, it can make airflow in the jetstream more likely to loop and bulge, causing the kinds of swirling eddies that result in blocking events.

Both the researchers’ observations and their model simulations strongly supported the idea that sea ice declines are a major factor in the frequency of blocking events over Greenland. When the researchers made changes only to sea ice in their model, they found an immediate connection to increased blocking, which in turn has led to increased surface melt on the ice sheet.

The findings may help explain some of the unusual weather patterns that have been seen in both Europe and North America in recent years. High pressure systems over Greenland can have the effect of blocking polar jet stream flow over part of the North Atlantic, causing the jet stream to split into branches and bringing about all kinds of severe weather events as a result.

In 2007, a high pressure blocking system over Greenland caused a split in the polar jet stream over the northern part of the North Atlantic, which ultimately resulted in extreme rainfall and flooding in the UK.

“To a certain extent, those conditions were repeated in summer of 2012, when we had a record wet summer in the UK,” adds Hanna. “And of course that was the year of the record high blocking conditions and extreme high temperatures and surface melt in Greenland.” 

So in this way, climate-induced changes in Greenland are not just causing problems locally - they’re creating mayhem throughout the North Atlantic, an example of the far-reaching influences of climate change and the interconnected nature of oceanic and atmospheric conditions around the world.

Greenland, of course, remains of prime concern thanks to its potentially devastating contributions to future sea-level rise. And, unfortunately, as more sea ice melts away, conditions are only likely to worsen, Francis said.

“It won’t be increased every single year, but the trends should continue downward — which isn’t good, because as we lose that ice that’s sitting on land on the Greenland island, it goes straight into the ocean and of course is one of the main contributors to sea-level rise,” she said. “That’s an effect that is felt all over the world.”