Global warming: the science is loud and clear

by
12 October 2018

Emily Shuckburgh gives a scientific account of how and why the climate is changing, and explains why it is not too late to act

Norwegian Polar Institute/PA

A polar bear wanders on thinning sea ice in the Arctic in August last year

A polar bear wanders on thinning sea ice in the Arctic in August last year

THE searing heatwave we experienced in the UK this summer may have contributed to as many as 700 deaths, preliminary analysis suggests. That is almost twice the number of people estimated to have died during the swine-flu epidemic in 2009. Science tells us that climate change made the heatwave at least twice as likely to occur.

The devastation wrought by flooding in recent years on communities across the UK, from Appleby to Tewkesbury, has been shocking. Entire towns and villages have been faced with rebuilding lives and livelihoods after homes and businesses were inundated. The winter floods of 2015 to 2016 are estimated to have cost more than £1.5 billion. Science tells us that climate change made Storm Desmond, which hit Cumbria and other areas in 2015, about 80 per cent more likely to occur.

In 2016, a severe drought in Southern Africa meant that millions of people needed humanitarian assistance in countries such as Malawi. On the other side of the world, South-East Asia experienced record-breaking heat: temperatures in Thailand soared above 40ºC.

Last year, Hurricanes Harvey, Irma, and Maria battered the Caribbean and southern United States. Science tells us that climate change made Hurricane Harvey both more likely and more intense, and the resulting damage worse.

THIS is our reality in 2018: a planet on which climate change, in all regions, is stoking the weather to increasingly destructive effect. Temperatures have increased substantially over the past century, and especially over the past 50 years. The past three years rank as the warmest on record, and the decade is on course to be the fourth in a row of record-breaking warmth.

Today, the world is more than 1°C hotter than it was in Victorian times. Other observations, including the warming of the oceans from the surface to the depths, and reductions in ice and snow cover, provide further evidence that planetary-scale warming is taking place.

The scientific evidence is clear as to the dominant cause: greenhouse-gas emissions. Fossil fuels — coal, oil, and natural gas — release carbon dioxide into the atmosphere when burned. The clearance of forests, agriculture — including industrial farming methods that damage soils, and industrial processes such as cement production — also generate greenhouse gases.

PAReservoirs such as Howden reservoir, at the top of the Derwent Valley, in the Peak District, begin to show cracks during the heatwave in 2018

IN 1992, in response to rising concerns about the dangers ahead, governments established the United Nations Climate Convention. In its most important clause, governments pledged themselves to “avoid dangerous anthropogenic interference with the climate system”: in other words, avoid dangerous human-induced climate change.

At the time, what “dangerous” meant was not clear. For years, politicians interpreted the danger level as 2ºC. Then came the Paris climate summit of 2015, when vulnerable developing countries insisted that 2°C was too high: impacts that were dangerous to their societies were already occurring, they argued, and the guardrail needed to be 1.5°C at the most.

The target was included in the Paris Agreement. And, at the summit’s conclusion, governments commissioned the Intergovernmental Panel on Climate Change (IPCC) to produce an assessment about why 1.5°C matters, giving as much detail as possible on the difference in impacts that we can expect at 1.5°C as opposed to 2°C. This week, it announced its conclusions.

Warming of 1.5°C rather than 2°C would, for example, mean a reduction in heat-related illness and deaths. Global sea-level rise would probably be about 10cm lower in 2100, exposing 10 million fewer people to related risks. It is thought that virtually all coral reefs would be lost at 2°C, while a small portion would remain at 1.5°C. Between two and three times more plants and animals are expected to experience severe habitat loss at 2°C, compared with 1.5°C.

The chances of catastrophic changes, such as the loss of ice sheets in Greenland or Antarctica, the massive release of methane from the thawing of vast frozen stores in the Arctic, or the turning of parts of the Amazon rainforest into savannah, are also much reduced if warming is kept to 1.5°C.

So it is clear that a 1.5°C world would be both more pleasant than one that was half a degree warmer still, and safer from potentially disastrous runaway impacts.

EVEN now, as the IPCC report confirms, climate change is proving a massively disruptive force — not least to nature. It is causing shifts in the conditions that sustain many species. These include changes in temperature, the length and timing of the seasons, and the availability of water. In the UK, familiar signs of spring — flowers blooming, trees coming into leaf, birds nesting, frogs spawning — happen days or even weeks earlier than 30 years ago. Mammals that rely on hibernation, such as hedgehogs, dormice, and bats, are reducing their period of hibernation, which is affecting breeding success and survival rates.

As a further consequence of carbon-dioxide pollution, the oceans are rapidly becoming more acidic. Comparable rates of ocean acidification have not been seen for many millions, perhaps hundreds of millions of years. Many marine species, including oysters and clams, are directly affected by ocean acidification, and it may indirectly affect fish populations.

Coral reefs are particularly vulnerable, and suffer from both ocean acidification and bleaching, which is a result of warming seas. The oxygen concentration is falling in many parts of the ocean, driven once more by climate change.

Under natural conditions, many species would be able to cope with gradual climate change and adapt accordingly. But rapid changes create unprecedented challenges for wildlife, especially when combined with the loss of natural habitats owing to agriculture and urbanisation. Entire food webs may be affected: for example, damp-loving insects suffer from rising temperatures and drought, in turn putting pressure on bird populations such as the song thrush, blackbird, ring ouzel, and golden plover which feed on them.

As the rate of loss and extinction continues to increase, future generations may inherit a world that lacks the incredible wildlife diversity that we enjoy today, and be poorer for it.

 

I AM a polar scientist. I study the polar regions, which are places of immense wonder and beauty, but also places that are changing rapidly, providing a warning for the rest of the world.

The Arctic has had greater warming than anywhere else to date. Arctic sea-ice coverage — measured from space by satellites — is plummeting. In late summer, the region of frozen sea is now less than two-thirds the size it was at the end of the 20th century. That is a drop equivalent to the area of the UK, Ireland, France, Spain, Germany, and Italy put together. Just imagine that size, covered in ice just a few decades ago, now gone.

Kieran Doherty / OxfamPastoral farmers living in the Somali region of Ethiopia have been hit hard by climate change and must travel with livestock to find pasture. “Sometimes I go four to five days without food,” Mahamud told Oxfam. “We don’t drink much. We take a few sips each day to moisten our throat. I’ve had difficult times. I can’t describe in words. You just try to keep going to find water and food.”

People who live in the Arctic describe the changes that they are seeing in their daily lives, as warming turns their icy wilderness to mud.

I visited the Canadian Arctic a few years ago. Unsurprisingly, when lives are intimately connected to the landscape, many are finding the rapid changes deeply unsettling. One lady told me that it is as if a friend whom they could trust had suddenly started acting strangely. She described many small details, such as robins singing on the roof of her house (striking because they are not usually found so far north), which combine to provide a perplexing picture of a society and a habitat in flux.

The polar regions also provide us with compelling evidence of how unnatural the current changes in climate are.

Antarctica is always so cold that, as snow falls, it piles up, layer on layer, trapping within it tiny bubbles of air. This means that, if we drill down through the ice, we can recover ancient air going back almost a million years. From this, we can see how the atmosphere and climate varied in the past.

The record shows that carbon dioxide in the atmosphere fluctuated between about 180 and 280 parts per million as the earth’s orbit around the sun slowly varied, driving us back and forth between Ice Ages and warmer periods. This is the slow cycle of natural climatic change. An extremely rapid, Industrial Revolution spike has put today’s carbon-dioxide levels at an incredible 405 parts per million. This recent change clearly lies far outside the natural cycle.

Perhaps most important, however, is the impact that disruption to the polar regions could have on the rest of the planet. Greenland and Antarctica are covered in vast ice sheets. These sleeping giants, if they melted, could transform our world through rising seas.

Evidence suggests that even a modest temperature rise may threaten these frozen reservoirs. Records indicate that, at a time just under half-a-million years ago, when temperatures were perhaps only slightly warmer than today, a large part of Greenland was ice-free, and sea levels rose to be more than six metres higher than they are now.

Melting has been seen across more than half the Greenland ice sheet during some recent summers, emphasising the current threat. The edge of the West Antarctic ice sheet is below sea level; so it is vulnerable to warm ocean waters encroaching beneath it. This is already happening, and there is evidence that key glaciers that are critical to the ice sheet’s stability may already be in unstoppable retreat.

Such changes to the polar ice sheets, which, it is thought, could be triggered at somewhere around 1.5°C to 2°C of global warming, would cause the seas eventually to rise by metres. This would transform global coastlines. A glance at a map of the world’s biggest cities shows that the majority are in coastal regions. Just a few tens of centimetres of sea-level rise, especially in combination with heavy rain and storm surges, could destroy buildings and displace hundreds of millions of people; the impact of substantial loss of the polar ice sheets would be catastrophic.

Thus the polar regions provide a loud siren in terms of the changes that are presmt now, how unusual they are in history; and what may be in store for us in the future.

 

CLIMATE change poses a truly global challenge, which no single country on its own can solve. The implications of climate change itself, and of the responses to it, are so wide-ranging that it cannot be addressed independently of sustainable development and efforts to eradicate poverty.

Limiting global warming to 1.5°C compared with 2°C would reduce challenging impacts on human health and well-being, and on ecosystems, making it easier to deliver the United Nations Sustainable Development Goals.

The amount of carbon dioxide that can be released before dangerous levels of warming are reached can be seen as a “carbon budget”. The more emissions we generate now, the faster we will have to slash them later to stay within the budget; and we may find that the speed of cuts then required is unachievable, even with new technologies. As a measure of the urgency, at the present rate of fossil-fuel use, deforestation, and soil damage we are on course to exhaust the budget that gives a good chance of staying below 1.5°C within the next ten to 15 years.

The central message of the IPCC’s report this week is that keeping temperatures below 1.5°C requires reducing carbon-dioxide emissions rapidly and dramatically to reach “net zero” by about 2050 — and significantly reducing other greenhouse-gas emissions at the same time. Long-term impact, such as rising sea levels, can be minimised only by a sustained commitment to net-zero greenhouse-gas emissions.

There exist great opportunities for making sensible changes that tackle climate change and address some of the other challenges that we face as a society — changes that reduce pollution, improve people’s health, create new jobs, support the poorest in our communities, and help preserve our natural world.

The science makes it clear, however, that the scale and urgency of the task are great. Although that leaders of virtually all countries agreed, in 2015, to attempt to keep global warming to 1.5°C, the world is currently on a pathway to reach 3°C by the end of the century. Over the next few decades, substantially greater cuts in emissions than have currently been pledged will be required to limit the impacts of climate change.

Lest there be any doubt, the IPCC has just made it clear that it is abundantly worth doing — and, with enough will, just possible.

Dr Emily Shuckburgh is a climate scientist and mathematician at British Antarctic Survey.

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