Analysis

Polar bears and climate change: What does the science say?

  • 04 Mar 2015, 13:45
  • Roz Pidcock

We've all seen the pictures of polar bears stranded on sea ice. They're  all too often used as the iconic poster animals of a rapidly changing climate.

Every now and again, claims emerge in the media that polar bears' plight might not be so serious after all. Just recently, Peter Hitchens said in the  Mail on Sunday polar bears are "doing extremely well right now" and that claims otherwise are "just hot air".

Carbon Brief has dug through the literature and spoken to polar bear experts. While little is known about some remote bear populations, it's clear there's no scientific basis for such optimism. As temperatures rise, polar bears face a bleak future ahead, scientists tell us.

Claims about polar bears on the up

The crux of Hitchens' argument is that polar bear numbers are rising around the world, not falling. He quotes biologist  Dr Susan Crockford, who says:

"On almost every measure, things are looking good for polar bears ... It really is time for the doom and gloom about polar bears to stop."

                                       Screenshot 2015-03-04 14.42.14

Source: Ben Webster, The Times,  Feb 27th 2015

This stems from a report authored by Crockford and published last week by the Global Warming Policy Foundation, a climate skeptic think tank. Entitled, "  20 good reasons not to worry about polar bears", the report describes itself as a "resource for cooling the polar bear spin".

The Times quoted the report's conclusion that:

"Polar bears are not currently threatened with extinction due to declining sea ice, despite the hue and cry from activist scientists and environmental organisations."

Similarly, a Mail on Sunday  article from last September, also featuring Crockford, claimed: "The poster boys of climate change thrive in the icy Arctic: Polar bears defy concerns about their extinction."

So, what is the evidence for the claims? And do other scientists agree there's no cause for alarm?

Read more

Leaf-eating insects may limit how much carbon forests absorb, study says

  • 03 Mar 2015, 17:20
  • Robert McSweeney

Forest tent caterpillar | Mary Jamieson

Insects could restrict how well trees absorb and store carbon in the future, according to a new study. In experiments simulating carbon dioxide levels in 2050, insects munched their way through almost double the number of leaves than under current conditions.

With fewer leaves, the trees are likely to become less effective at absorbing carbon dioxide from the air, the researchers say.

Carbon dioxide fertilisation

Trees are the biggest carbon sink on land. Through a process known as photosynthesis, trees convert carbon dioxide, water and sunlight into the fuel they need to grow, locking up carbon in their trunks and branches as living biomass.

Research suggests that when there's more carbon dioxide in the air, trees grow more quickly because the rate of photosynthesis speeds up. This is called 'carbon dioxide fertilisation'.

Scientists expect that as human-caused carbon dioxide emissions increase, forests will absorb and store more carbon, assuming they have enough water and nutrients to grow.

But the results of a three-year experiment, just published in Nature Plants, suggests that insects, such as caterpillars, may make it harder for trees to absorb this extra carbon by munching their way through the trees' leaves. With fewer leaves to absorb sunlight, the trees can't photosynthesise as much, and they absorb less carbon dioxide from the air.

'Double whammy'

The researchers set up their experiment at the Aspen FACE facility (Free-Air Carbon Dioxide Enrichment) in Wisconsin in the northern US. At the facility, birch and aspen trees are surrounded by vertical vents that release different gases to simulate future conditions.

FACE Aerial 2005 -25

Read more

Scientists discuss the role of climate change in the Syrian civil war

  • 02 Mar 2015, 20:00
  • Robert McSweeney

Aleppo, Syria in 2013 | Shutterstock

This month will see the civil war in Syria reach an inauspicious fourth birthday. Since the uprising in 2011, over 220,000 people have been killed and almost half the Syrian population have fled their homes.

Evidence suggests the conflict was triggered by a complex mix of social, political, economic and environmental factors. But new research finds that human-caused climate change could also have had an influence.

The study, published in the Proceedings of the National Academy of Sciences, suggests a severe drought that began in 2006 was a catalyst for the conflict, and that climate change has made such droughts in the region more than twice as likely.

Syrian conflict

On 15th March 2011, Syrian security services opened fire on pro-democracy protesters in the southern city of Dara'a, killing several people. The unrest that followed spread throughout the country over the ensuing months, and by February 2012, Syria had descended into civil war.

A study published last year found that a multi-year drought contributed to food shortages, urban migration, and unemployment in the run up to the conflict.

Now the new study says the drought had a catalytic effect on the unrest in Syria, and human-caused climate change has made the chances of such a severe drought between two and three times more likely.

Prof Richard Seager, a climate scientist at Columbia University and co-author on the new study, explains:

"We're not saying drought caused the war. We're saying that added to all the other stressors, it helped kick things over the threshold into open conflict. And a drought of that severity was made much more likely by the ongoing human-driven drying of that region."

Multi-year drought

Syria sits in a band of relatively moist and productive land in the Middle East, known as the Fertile Crescent. But between 2006 and 2010, the region was hit by the worst multiyear drought since 1940.

Syria gets almost all of its rain during its six-month winter, from November to April. In 2007-08, winter rainfall across Syria fell by a third, with some areas receiving no rain at all. The winter was the driest in the observed record, the researchers say.

The decreasing rainfall (shown in the top graph below) combined with rising temperatures (second graph) resulted in a decline in soil moisture (third graph), the researchers say. This had dramatic consequences for Syrian agriculture.

Kelley Et Al (2015) Syria Fig1

Read more

New study directly measures greenhouse effect at Earth’s surface

  • 25 Feb 2015, 18:00
  • Robert McSweeney

Cloudy skies | Shutterstock

Scientists know that greenhouse gases in the atmosphere cause the Earth to warm. But measuring exactly how much heat they trap is harder than you might think.

Previous studies using satellites have established that more heat is entering the atmosphere than leaving it. But a new study goes a step further and directly measures the amount of warming greenhouse gases are producing at Earth's surface.

The paper provides the critical link between rising carbon dioxide concentrations and the extra energy trapped in the climate system, the researchers say.

Greenhouse effect

Joseph Fourier first suggested in the 1820s that gases in the Earth's atmosphere trap heat and help keep the planet warm, coining the term greenhouse effect. Physicist John Tyndall later extended the theory by identifying the gases, such as carbon dioxide and methane, that were responsible for the warming.

Jumping forward a century and a half, we now know a lot more. Using satellites to measure how much of the sun's energy enters the Earth's atmosphere, and how much is reflected or re-emitted back into space, scientists have shown that the difference between the two is increasing. This means the Earth is trapping more heat than it used to, and therefore must be warming.

But while those studies show a widening gap between the energy reaching and leaving Earth, they are unable to directly measure how much warming greenhouse gases are causing at a particular point in time. New research, published today in Nature, shows how scientists have directly been able to measure the warming effect of greenhouse gases at Earth's surface.

Measuring energy

The researchers used a set of instruments to take thousands of measurements at the Earth's surface. The instruments record the longwave energy that is re-emitted by greenhouse gases back towards the Earth's surface, which causes the warming.

Making these sorts of measurements on the ground is difficult, says lead author Dr Daniel Feldman, a geological scientist at the Lawrence Berkeley National Laboratory in the US. With weather systems passing overhead, and temperatures and humidity changing frequently, it's tricky to take energy measurements without other factors getting in the way.

To overcome this problem, the researchers measured temperature and water vapour at the same locations so that their influence on warming could be eliminated from the calculations, leaving just the impact of greenhouse gases.

The scientists used data from 2000 to 2010, collected from two sites in the US: the southern Great Plains and northern Alaska. They chose these sites because of their very different climates, says Feldman. This meant the researchers could investigate both a mid-latitude and a high-latitude location.

Read more

Surface warming 'hiatus' could stick around another five years, say scientists

  • 23 Feb 2015, 16:30
  • Roz Pidcock

Don't be surprised if the slower pace of warming we're seeing at the Earth's surface lasts for another five years, scientists say.

new paper out today puts the chances of the so-called "hiatus" staying until the end of the decade at about 15 per cent, or one in six.

But the heat hasn't gone away. The scientists say most of it is lurking in the deep ocean and we can expect the pace of warming to pick up when this heat gets released again.

Slower surface warming

Since 2000, the temperature at the Earth's surface  hasn't warmed as quickly as it has in previous decades, despite greenhouse gas emissions rising  faster than they were before.

A growing body of evidence is  homing in on the  Pacific Ocean as the main culprit for why we're seeing "unexpectedly modest" warming, as the Nature Climate Change paper puts it.

Scientists think a natural fluctuation is causing heat to find its way to the deep ocean in the Pacific, where it doesn't warm the atmosphere as much it would if it stayed at the surface.

A number of recent studies have found that periods of faster and slower warming  aren't unusual in Earth's temperature record. It's what scientists expect as these natural cycles flip-flop between their  different phases, superimposed on top of greenhouse gas warming.

But what are the chances of natural variability being strong enough to offset some, or even all of the warming expected from greenhouse gases?

The new paper by Dr Chris Roberts, an ocean and climate specialist at the Met Office Hadley Centre, and colleagues at the University of Exeter sheds some new light on this question.

Odds of a 'hiatus'

The new paper uses a suite of climate models to examine past temperatures with and without greenhouse gas forcing. The authors find there's a 28 per cent chance natural variability could cause a five-year long 'hiatus'.

The scientists define 'hiatus' as a period during which the observed temperature rise is less than the warming expected from greenhouse gases of 0.2 degrees Celsius per decade.

Read more

Uncertainty behind climate projections could be cut in half by 2030, study shows

  • 23 Feb 2015, 16:00
  • Robert McSweeney

Smoke stacks | Shutterstock

Scientists will soon be able to forecast climate change more accurately, according to new research. Projections of future temperature rely on estimates of how sensitive the Earth's climate is to rising emissions, and the uncertainty in those estimates could be halved within 15 years.

More certainty about the climate's sensitivity to emissions means a better assessment of our chances of keeping global temperature rise below the two-degree limit, the researchers say.

Climate sensitivity

Climate sensitivity is the amount of warming we can expect when carbon dioxide in the atmosphere reaches double the level before the industrial revolution. On current emission trends, we're set to reach that point shortly after 2050.

There are two ways to express climate sensitivity. Equilibrium Climate Sensitivity (ECS) refers to the total amount of warming once the Earth has had time to adjust fully to the extra carbon dioxide. ECS allows for 'feedbacks' in the climate system that can amplify or slow the pace of warming, many of which act over decades or even centuries.

An alternative option is the Transient Climate Response (TCR), which is the warming at earth's surface we can expect at the point of doubling. This doesn't take into account long term feedbacks, and so estimates of TCR are lower than for ECS.

In its 2013 report, the IPCC estimates TCR is likely to lie between 1.0 and 2.5 degrees Celsius. The new research, published in Nature Geoscience, suggests scientists will be able to reduce the uncertainty around these estimates by about 50 per cent by 2030.

Bigger proportion

The new paper deals with one way to estimate TCR, which is to compare how much greenhouse gases have risen over the industrial period with observations of how much the temperature has changed in that time.

But factors such as aerosols and other greenhouse gases have contributed to the observed temperature change, making it difficult to calculate TCR from historical observations.

Aerosols are released into the atmosphere when fossil fuels are burned. These tiny particles have a direct effect on temperature by scattering sunlight, and an indirect effect by stimulating cloud formation, preventing sunlight reaching Earth's surface.

Although scientists know that aerosols have an overall cooling effect on the climate, they aren't as certain about the size of the temperature effect as they are for carbon dioxide.

But uncertainty over aerosols is set to be less of a problem in the near future, the study says.

While emissions of carbon dioxide are expected to rise in the next few decades, emissions of aerosols and other greenhouse gases are expected to slow, or fall. This means carbon dioxide will make up a bigger proportion of the human-caused factors affecting the climate.

You can see this in the graph below: the influence of carbon dioxide on the climate (red line) is projected to increase more rapidly than aerosols and other gases over the next 15 years (blue and green lines).

Read more

New satellite reveals places on Earth most at risk from ocean acidification

  • 17 Feb 2015, 13:15
  • Roz Pidcock

Images beamed back from space are helping scientists monitor how vulnerable the world's oceans are to human pressures. As the level of carbon dioxide in the atmosphere rises, it gets absorbed into the oceans, making them more acidic.

Ocean acidification is a serious but often overlooked concern facing the world's oceans and the ecosystems that depend on them, say the researchers.

The international team of scientists published some of their early findings and images in the journal Environmental Science and Technology today.

Acidifying oceans

quarter of the carbon dioxide released into the atmosphere dissolves into our seas. This changes the seawater chemistry, making it more acidic. This is known as ocean acidification.

Since the start of the industrial era, the pH of ocean surface water has dropped by 0.1, equivalent to a  26 per cent increase in acidity.

But acidification isn't happening at the same pace everywhere, some places are acidifying faster than others. Observing the earth from space using satellites can help identify which regions on Earth are most at risk from ocean acidification.

Alkalinity From Space

A global map of total ocean alkalinity, an indication of the sea surface's ability to buffer itself against ocean acidification. Credit: Ifremer/ESA/CNES

Read more

Reaction: Geoengineering is no substitute for cutting carbon emissions, conclude US researchers

  • 11 Feb 2015, 16:30
  • Robert McSweeney

Above and below clouds | Shutterstock

On Tuesday, the US National Research Council published two new reports on 'climate interventions', or what's more commonly known as 'geoengineering'.

Geoengineering is the deliberate large-scale intervention into the Earth's climate system to try and limit the effects of human-caused global warming, and it can be divided into two main areas Removing carbon dioxide from the atmosphere, sometimes known as Carbon Dioxide Removal (CDR), is one approach. The other is reflecting some sunlight away from the Earth before it can be trapped by greenhouse gases, referred to as 'albedo modification' in the reports, but more commonly known as Solar Radiation Management (SRM).

The new reports are the result of an 18-month study into the potential impacts, benefits and costs of geoengineering. The study produces a set of recommendations, which call for more research and development, but also caution that sunlight-reflecting technologies "should not be deployed at this time".

Geoengineering Summary Table

Overview of general differences between carbon dioxide removal approaches and albedo modification approaches. Source: US National Research Council ( 2015)

While the reports make clear that geoengineering is not a substitute for global action to reduce carbon emissions, it recognises that some action may be necessary to avoid the worst impacts of climate change.

The reports have prompted a flurry of reaction, particularly in the US. Here are some of the selected highlights.

Read more

Aerosols dampen pace of Arctic warming for now, say scientists

  • 11 Feb 2015, 11:00
  • Robert McSweeney

Arctic sea landscape | Shutterstock

As the Earth warms under increasing greenhouse gas emissions, temperatures have risen more quickly in the Arctic than the rest of the world. But particles emitted as fossil fuels are burned mask a lot of that warming. Without them, the temperature rise in the Arctic would be more than double what we've seen in the past century, a new study finds.

But it's no good news story, those same particles are responsible for causing air pollution in cities across the world.

And with air pollution set to fall while greenhouse gases continue to rise, we could soon see a faster rate of warming in the Arctic, the lead author tells Carbon Brief.

Twice as fast

Temperatures in the Arctic are increasing more than twice as fast as the global average. This is known as Arctic amplification. A primary cause is diminishing Arctic sea ice: as the ice melts, energy from the sun that would have been reflected away is instead absorbed by the ocean.

A new study, just published in Nature Climate Change, works out the specific contributions from different influences on temperatures in the Arctic, including natural factors.

Humans can affect the climate in contrasting ways. The planet warms as extra greenhouse gases in the atmosphere trap more heat. But at the same time, other tiny particles and gases known as aerosols are having an overall cooling effect.

The particles have a direct effect on temperature by scattering sunlight, and an indirect effect by stimulating clouds to form, preventing sunlight reaching Earth's surface.

Some sources of aerosols are natural, such as volcanoes and chemicals released by tiny sea creatures. However, since the industrial revolution, humans have been emitting more and more aerosols through vehicle exhausts and burning fossil fuels and wood.

Read more

US flooding on the rise in a changing climate, study shows

  • 09 Feb 2015, 16:05
  • Robert McSweeney

The central US is experiencing flooding more often now than it was 50 years ago, new research shows. The study across 14 states finds rivers over much of the region are breaching their banks more frequently, leading to a greater number of floods.

The researchers attribute the increase in flooding to rising temperatures in the region and more days with heavy rainfall.

Serious flooding

In recent decades, the central US has been hit by a number of serious and widespread floods. Flooding in the spring of 1993 and summer of 2008 affected as many as ten states, for example. The disaster saw hundreds of counties declared Presidential Disaster Areas, giving them access to emergency relief funding.

Scientists have since been trying to work out whether floods are getting worse or if what we're seeing in this part of the US is down to natural variability.

To investigate changes in river flooding, scientists look at historical records of river flow and the maximum amount of water they can hold before overflowing. The flow, or 'discharge', of a river is measured by instruments at different points along its course.

Studies in the past have found the maximum flow through rivers hasn't changed much over the late twentieth and early twenty-first centuries. But a new study, published in Nature Climate Change, finds that rivers are hitting these high flows more often.

More frequent peaks

The researchers analysed records of river flows from 774 instrument stations across the central US, from North Dakota to West Virginia. They counted how many times each river hit a point where there was so much water flowing through it that it was likely to cause a flood.

Read more