Warming oceans
As countries grapple with intense marine heat waves and stronger storms, the latest IPCC report says climate change has already altered our oceans, polar regions and high snowy mountains
As intense marine heatwaves become frequent, glaciers are melting like never before
THE TIMING could not have been more coincidental. As the ocean off the western coast of North America warms up at an unusually rapid pace, triggering fears of drought and warnings of harm to salmons, sea lions and other marine life, the Intergovernmental Panel on Climate Change (IPCC) has released a report that says marine heat waves have become twice more frequent in the past four decades and are lasting longer.
“The world’s ocean and cryosphere have been ‘taking the heat’ from climate change for decades, and consequences for nature and humanity are sweeping and severe,” Ko Barrett, vice-chair of IPCC, said while releasing the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCCC). Prepared with reference to
7,000 scientific publications, SROCCC is the first such report to look into the impacts of climate change on the planet’s vast oceans and fragile ice sheets, which are home to some 1,500 million people and influence everything from climate and energy to trade, transport and culture worldwide. “The rapid changes to the ocean and the frozen parts of our planet are forcing people from coastal cities to remote Arctic communities to fundamentally alter their ways of life,” said Barrett.
The report finds that human activities are responsible for 84 to 90 per cent of the marine heat waves that occurred in the last one decade, and says the ocean will continue to warm throughout the 21st century. By 2081, the frequency of marine heat waves could jump by 20 to 50 times.
These events would particularly become frequent in the Arctic and tropical oceans. Since ocean warming reduces mixing between water layers and, as a consequence, the supply of oxygen and nutrients for marine life, marine heat waves will have disastrous effects on several ecosystems as well as economies. For instance, in 2014-15, when the northern Pacific Ocean had seen such unusually warm water, it had boosted the growth of toxin-producing algae and suppressed the growth of small organisms at the base of the ocean food chain. The impacts rippled through ocean ecosystems, with mass die-offs of salmon, seabirds and other marine mammals, and the closure of several fisheries.
But a more pronounced effect of such marine heat waves would be on wind circulation. The direct cause of heat is weak winds. And, as the report indicates, the Atlantic Meridional Overturning Circulation (AMOC), which ensures northward flow of warm, salty water in the upper layers of the Atlantic and a southward flow of colder, deep waters, has already weakened. Any substantial weakening of the AMOC would cause further decrease in marine productivity in the North Atlantic, more storms in Northern Europe, less Sahelian summer rainfall and South Asian summer rainfall, a reduced number of tropical cyclones in the Atlantic and an increase in regional sea level along the northeast coast of North America, the report warns.
SLOW WIND SPEED was a reason behind intensification of extremely severe cyclone Fani, of category 4, which battered the eastern Indian coast in May this year. SROCCC says there is an emerging evidence of an annual increase in percentage of category 4 and 5 storms in recent decades. These storms further sustain their strength by feeding on the moisture over warm ocean waters. The link became evident during late September, when in a rare occurrence, tropical storm Lorenzo waltzed across the unusually warm northeastern Atlantic Ocean for a few days and then evolved into a category 5 hurricane.
In the absence of an El Niño event, the World Meteorological Organization (WMO) has already hinted at global warming as a cause of current increase in sea surface temperatures around the world. Its warning sits well with long-term ocean warming trend observed by SROCCC, which says from 1993 to 2017, both the rate of ocean warming and the amount of heat intake up to a depth of 2,000 m, have doubled as compared to the 1969-1993 period. By 2100, this figure could increase up to five to seven times.
Along with the expansion of warmer ocean, growing water inputs from ice sheets in Greenland and Antarctica, and meltwater from glaciers in polar and mountain regions are contributing to an in
FROM 1993 TO 2017, BOTH THE RATE OF OCEAN WARMING AND THE AMOUNT OF HEAT INTAKE UP TO A DEPTH OF 2,000 METRES HAVE DOUBLED AS COMPARED TO THE 1969-1993 PERIOD
creasing rate of sea level rise. While the sea level rose globally by about 15 cm during the 20th century, it is now rising twice as fast and could reach up to 60 cm by 2100, even if greenhouse gas emissions are sharply reduced and global warming is limited to below 2oC.
However, the report warns, sea level rise could reach 60 to 110 cm if emissions continue to increase strongly. “The more decisively and earlier we act, the more able we will be to address unavoidable changes, manage risks and achieve sustainability for ecosystems,” says Debra Roberts, co-chair of IPCC Working Group II.
These were also the concerns highlighted in the United in Science report, prepared by the world’s leading climate science organisations for the UN Climate Action Summit (UNCAS), held in New York on September 23. The report calls for a five-fold increase in nationally determined contributions (NDCs), volunteered by countries under the 2015 Paris Agreement, to limit global warming to within 1.5oC above pre-industrial levels and a threefold increase to stay below 2oC rise. AHEAD OF THE summit, UN Secretary General Antonio Guterres had called on world leaders, private companies and international organisations to come to UNCAS with enhanced commitments. But expectations dampened when four of the top 15 highest net emitters of greenhouse gases—the US, Japan, Brazil and Australia—refused to revise their commitments and the oil-rich Saudi Arabia and South Africa did not participate. Most countries only announced to boost their national action plans. China said it would pursue a path of low-carbon development and announced naturebased solutions that could unlock up to 12 billion tonnes of global emissions reductions and removals annually. The EU announced to devote 25 per cent of its next budget on climate related activities. Prime Minister Narendra Modi reiterated India’s previous commitments to combat climate change and announced a new target of achieving 450 GW renewable energy without giving a specific date for the same. Though 65 countries committed to enhance their NDCs and cut greenhouse gas emissions to net zero by 2050, it did not raise the global commitment even by three-fold. “At the current rate of emissions the world can end up with an average warming of anywhere between 2.7oC and 3.7oC which would have devastating impacts, especially on the oceans,” Guterres said.
“You are failing us. But young people are starting to understand your betrayal. The eyes of all future generations are upon you, and if you choose to fail us, I say, we will never forgive you.” This was 16-year-old Swedish climate activist Greta Thunberg’s appeal to world leaders at the summit. The world leaders’ response to her appeal was little more than business as usual.
AT THE CURRENT RATE OF EMISSIONS, THE WORLD CAN END UP WITH AN AVERAGE WARMING OF ANYWHERE BETWEEN 2.7OC AND 3.7OC, WHICH WOULD HAVE DEVASTATING IMPACTS