According to an authoritative new report, some of the heat that accumulates in oceans over the years can get released back to the atmosphere. In a nutshell, the oceans were behaving less like heat sponges over the last year or more, instead releasing heat to the surface, and hence the spike in average global temperatures.
Global temperatures have spiked again. The earth has been on a streak – the last 11 months have been the hottest ever in history.
We are in October, but much of India continues to be suffocatingly hot and muggy, mirroring the extraordinary warming that continues to bedevil the planet.
Globally, every single of the last 11 months, starting from October 2015, have been the hottest ever recorded in terms of monthly temperatures, since fairly comprehensive instrumental measurements began to be taken in 1880. A run of this duration has never happened before.
There has also been a spike in global average temperatures over the last couple of years.
Unlike what one may imagine – with global warming, surface temperatures do not incline smoothly upwards like a ramp; they tend to jump in spurts. Climatologist Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research in the US, put this succinctly a few years ago:
“With global warming, you don’t see a gradual rise from one year to the next. It’s more like a staircase. Nothing much happens for ten years. Then you suddenly have a jump and things never go back to the same level again.”
Well, we just jumped. A couple of years ago, the globe was at about 1 degree Celsius above the 1880-1920 average. We’re currently 1.3°C above that. A rise of every tenth of a degree is non-trivial and three-tenths is huge. Moreover, the rise took place over an already high level in 2014: that year saw record average temperatures, and we have gone even higher each year since. This begs a couple of questions: what has caused this warming? And what does it mean for our immediate future?
There are two increasingly interlinked causal factors: we just witnessed one of the strongest El Ninos – ocean currents going west along the equatorial Pacific that every few years reverse and move east – ever recorded, which lasted a year-and-a-half until mid-2016. Among other effects, El Ninos transfer warmer subsurface waters to the eastern Pacific surface, and impede colder subsurface water rising elsewhere, hence causing a two-pronged rise in global temperatures.
The second, indeed stronger factor underlying the ongoing record temperatures is sustained global warming. In this, the oceans play a crucial role, the significance of which cannot be overstated.
Most of the excess heat trapped by greenhouse gases is taken up by the oceans – 93%, the Intergovernmental Panel on Climate Change’s Fifth Assessment Report tells us, and as much as two-thirds goes into just the upper ocean layers, from 0-700 metres.
These upper layers of the oceans have taken up a jaw-dropping amount of heat, over 17 x 10^22 joules (that is 10 followed by 22 zeros) since 1971. Averaged out each year, this would amount to 40 times the entire annual energy consumption of the United States!
The third spike
This massive heat may not remain there permanently. An authoritative 460-page report released last month by the International Union for the Conservation of Nature, Explaining Ocean Warming, stated that some of the heat that accumulates over the years can get released back to the atmosphere. “In a strong El Nino year,” the report said, “this subsurface heat is suddenly transferred into the surface layer [the top 100 metres of the oceans] for release to the atmosphere.”
In a nutshell, the oceans were behaving less like heat sponges over the last year or more, instead releasing heat to the surface and hence the spike in average global temperatures.
What does this imply for the next few years? We can guess the answer by looking at our recent past.
The current spike is the third such in the last 40 years. There was one in 1976-77, when temperatures shot up by 0.3°C in a single year, going by NASA’s Goddard Institute temperature data. The second and most famous was in 1998, caused by the strongest El Nino of the 20th century.
After 1977, average temperatures fell the next year only to rise again and stay in that band. It is striking that average temperatures never fell below the 1977 peak after 1985. And after the 1998 jump, average temperatures fell by 0.2°C for a couple of years, but continued global warming ensured that temperatures rose again and stayed within that band until 2013. Even in this period of relatively flat growth, average temperatures exceeded 1998’s record in 2005, 2010 and 2014, El Nino or no El Nino.
Global temperatures this year will likely be about 1.25°C higher than the 1880-1920 average, said James Hansen of the Columbia University Earth Institute and others in a draft publication, Young People’s Burden: Requirement of Negative CO2 Emissions, placed in the public domain last week. So 2016 will end up as the hottest year ever, the third year in a row to get that tag, something that has never happened before.
Temperatures will likely dip slightly next year – yearly fluctuations are normal and expected. But the experience of the last two spikes suggests we will broadly remain around the 1.2-1.3°C band for the next few years. Until the next jump.
Searing worries for India
That we may stay in this warming range over the next few years is, or at least ought to be, deeply worrying for us in India, for many reasons. Barely tolerable even at current levels, incessant heat and more humidity – because warmer air holds more moisture – of the kind we have been struggling to cope with in Delhi and other cities these past few weeks, will stress people in urban areas.
Two, certain ecosystems and species that constitute them will be damaged because of temperatures persistently staying above what they are used to historically. In particular, the Indian Himalayas, where temperatures tend to rise at least twice above India’s average, have seen changes in the nature of precipitation, amount of rainfall, glacial melt, shifts in the altitudes of fruit and vegetables and the timing of flowering of plants, from Kashmir to Arunachal Pradesh.
Three, it would mean more drought and increasingly erratic rainfall, at a time when inter-state river conflicts are already at a flashpoint. Not every El Nino causes a drought in India, but every serious drought over the past few decades has happened during an El Nino. And El Ninos, according to the IUCN report, will increase in frequency and become more intense as warming continues.
As humans continue to recklessly use the oceans as a dump for heat and carbon dioxide, nature is telling clearly that there’s only so long we can continue to do so.
The author is a member of India Climate Justice. He works and writes on issues related to global warming.