​Aussie scientists give 1830 as the year when human-driven global warming kicked off

The world was going through a natural warming cycle in 1830.

The Tambora volcanic eruption in 1815 had suddenly altered global temperatures. This was so violent that 1816 became known as the “year without a summer”.

Like other mega-eruptions, Tambora had thrown so much ash into the atmosphere that it had cooled large parts of the northern hemisphere and entire seasons were skipped. This meant that by 1830 the world was warming to compensate — a system searching for its previous equilibrium.

But that warming didn’t stop as it naturally would have. Instead, it kept on accelerating. In the past decade, that acceleration has become stuck, with temperature records constantly tumbling.

The 1830 acceleration, according to Australian scientists, is the first indicator of global warming driven by humans. Known as anthropogenic warming, this comes about as a result of people burning fossil fuels.

The gases it releases get trapped in the atmosphere and drives the greenhouse effect. When more and more gets trapped, as humans burn ever increasing amounts of fossil fuels, it leads to profound heating of the planet.

Until now, scientists have generally taken the latter half of the 1800s as the starting point for anthropogenic warming. This would be about a century after the Industrial Revolution kicked off.

But new research, Early Onset of Industrial-era Warming across the Oceans and Continents, has shifted that date back. Published in the peer-reviewed journal Nature, it concluded: “Sustained industrial-era warming of the tropical oceans first developed during the mid-19th century.”

Starting in the northern hemisphere, where the Industrial Revolution was most intense, it then spread to oceans in the south.

That’s important because 90% of the heat that gets to the planet’s surface ends up in the oceans. They store this and normally that gradually alters their temperature over the course of centuries.

The only time when things naturally speed up is when El Niño or La Niña come along and quickly warm or cool large areas of water in the Pacific Ocean. That has a profound impact on the global weather system. The current drought in Southern Africa can be traced to El Niño flaring up.

Data to support the 1830 warming finding was taken from corals and fossilised marine animals. This allowed the Australian research team to go as far back as 1500 and create a long-term trajectory of ocean temperatures.

Accurate data records don’t go that far back. Generally, they date from the latter half of the 1800s.

As a result, scientists have normally taken the start date of global warming as close to the 1880 date for which their data started to be comprehensive. But that didn’t cover large parts of the southern hemisphere, for which data only started being kept later. In South

Africa, these records only start at the turn of the 20th century.

The researchers said this has a pro-found impact on our current understanding of global warming. Data from Nasa and other meteorological agen- cies showed that July was the hottest month ever recorded, 1.3°C above the 1880 date when records began. This year is predicted to be the hottest ever recorded, taking the title from 2015.

This brings large parts of the world perilously close to dangerous warming. At the COP21 climate change con- ference last year, countries passed the Paris Agreement. When it comes into legal force (probably in September), this will bind countries to the task of doing all that they can to ensure that global warming does not go beyond 2°C above pre-industrial levels.

That number is already too hot for many African countries and island states. The United Nation’s own climate body, the Intergovernmental Panel on Climate Change, said, to survive with intact ecosystems, these countries need to have warming kept below 1.5°C this century.

But the Australian research said that this figure has probably already been passed, if their 1830s date for anthropogenic global warming is factored into calculations.

So we are already living in a 1.5°C hotter world — a world in which much of Africa’s water dries up, rains become unpredictable and many crops wilt under the intense heat.

That makes tackling anthropogenic global warming all the more urgent.

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Sipho Kings
Sipho Kings is the acting editor-in-chief of the Mail & Guardian

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