Analysis

Scientists stay poised for imminent arrival of El Niño

  • 10 Oct 2014, 12:30
  • Roz Pidcock

The Pacific weather phenomenon known as El Niño looks to be firmly on its way. After a slow start, forecasters yesterday confirmed an El Niño should be making an appearance in the next month or two, though it's likely to be a weak one.

Pacific fluctuations

Every five years or so, a change in the winds causes a shift to warmer than normal ocean temperatures in the  equatorial Pacific Ocean - known as El Niño, or cooler than normal - known as La Niña, moving briefly back to normal in between.

The warm and cool phases together are known as the El Niño Southern Oscillation (ENSO), and are responsible for most of the fluctuations in global weather we see from one year to the next.

Each time a switch occurs, changes in the ocean and atmosphere above affect   global temperature and rainfall patterns worldwide.

ENSO

Sea surface temperature during El Niño (left) and La Niña (right). Red and blue show warmer and cooler temperatures than the long term average. [Credit: Steve Albers, NOAA]

 

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Behind the pictures: What does climate change mean for the walrus?

  • 08 Oct 2014, 16:36
  • Robert McSweeney

Group of walrus | Shutterstock

Last week the media was awash with pictures of a ' mass haul-out' of around 35,000 walrus on the shores of Alaska. The sight of so many walrus lounging on land rather than sea-ice led many to herald it as further evidence of climate change.

We take a look at what retreating sea-ice might mean for this iconic Arctic mammal.

Haul-out

Walrus are typically found in the shallow coastal waters of the Arctic circle, migrating with the sea-ice as it expands and contracts through the seasons. Walrus typically 'haul-out' by climbing onto sea ice and using it as a platform for feeding, resting and breeding.

There are two main types of walrus, Atlantic and Pacific, named after the oceans in which they're found. It was the latter that were captured on camera in such large numbers on the Alaskan coast last week.

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How air pollution caused Europe’s rivers to fill

  • 06 Oct 2014, 17:02
  • Robert McSweeney

River Wisla | Shutterstock

Air pollution from Europe resulted in a 25 per cent increase in river flows in Poland and Germany during the late 20th century, a new study finds. The researchers say their findings show how the impact of burning fossil fuels is not just limited to increasing temperatures.

Solar dimming

In the sixties and seventies, air quality across much of Europe was very poor. Coal power stations and inefficient cars belched out tiny particles, known as aerosols, into the atmosphere. These aerosols caused widespread health problems and contributed to the famous 'pea-souper' smogs in London.

This new piece of research, published in Nature Geoscience, finds that these aerosols also caused an increase in the amount of water flowing in rivers across Europe.

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

One type of aerosols, called sulphate aerosols, are emitted from cars and power stations. Once in the atmosphere, these aerosols affect the climate in two ways. They directly scatter sunlight and reflect it back out to space. They can also react with clouds in complex ways, causing the clouds to reflect more light back out to space. This process, known as 'solar dimming', reduces the amount of the sun's energy that reaches the Earth's surface.

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Scientists weigh in on two degrees target for curbing global warming

  • 02 Oct 2014, 13:15
  • Roz Pidcock

Yesterday, two scientists published a  stern critique of the longstanding target to limit global warming to two degrees above pre-industrial levels.

Branding the target "wrong-headed" and "tenuous", the authors argue we should ditch the two degree target in favour of a suite of "vital signs" that would let us track the Earth's health.

The  commentary, published in the journal Nature, has  generated a  certain  amount of  interest. We asked climate scientists for their thoughts.

Setting a target

In 1992, the United Nations Framework Convention on Climate Change (UNFCCC) decided the objective of global climate policy should be to stabilise humans' influence on the climate below the level at which it can be considered "dangerous".

As temperatures rise, so do the risks of climate change. As the recent report on climate change impacts from the Intergovernmental Panel on Climate Change (IPCC) puts it:

"Increasing magnitudes of warming increase the likelihood of severe, pervasive, and irreversible impacts."

With governments worldwide recognising the need to keep rising temperatures in check, it's important to have a goal, Professor Nigel Arnell, director of the Walker Institute for Climate System Research, tells us:

"When we're trying to work out what future climate change might do and how to reduce it, you need some form of metric or indicator on order to judge how well particular policies achieve that goal."

A good indicator

Curbing temperature rise has been central tenet of climate policy for two decades. One of Victor and Kennel's main criticisms in the Nature commentary is the international community's narrow focus on temperatures at earth's surface.

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How we can make good decisions about geoengineering

  • 30 Sep 2014, 15:15
  • Dr Rob Bellamy

NERC

Next month's synthesis report from the Intergovernmental Panel on Climate Change (IPCC) is due to give the organisation's verdict on geoengineering, a radical set of proposals to use large-scale technologies to tackle climate change.

There are two types of geoengineering. Carbon geoengineering seeks to remove carbon dioxide from the atmosphere, for example by capturing it from the air and storing it underground, or by adding iron to the oceans to trigger carbon-absorbing algal blooms.

Solar geoengineering is different. It seeks to reflect some sunlight away from the Earth before it can be trapped by greenhouse gases.This can be done, for example, by spraying clouds with sea salt to make them more reflective, or by stratospheric aerosol injection, where reflective particles are pumped into the atmosphere.

Geoengineering

My colleagues and I have been  examining the importance of 'opening up' discussion about geoengineering to alternative options, different perspectives and real world complexity.

'Closing down' assessment

Our earlier research has shown that the ways in which researchers frame assessments of geoengineering have important effects on the conclusions people come to.

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Get ready for hotter summers and more flooding in the UK, say scientists

  • 29 Sep 2014, 16:10
  • Roz Pidcock

Weather-wise, the UK saw it all last year. The coldest spring for 50 years, a sweltering summer heat wave and the wettest winter since records began. Today, a new report examines whether climate change is upping the odds of these events occurring.

The collection of papers, published in a  bumper edition of journal Bulletin of the American Meteorological Society, looks at 16 weather events that took place last year across the world. From Colorado to Korea, the scientists examine heatwaves, droughts, heavy rain and storms.

Human fingerprints

Globally, there is  evidence for changes in some types of extreme weather, and evidence for a human fingerprint in those changes. But different types of event are affected differently.

Climate change is greatly increasing the odds of heatwaves worldwide, today's report concludes. For storms, rainfall and drought the picture is less clear, however. Big differences between regions, natural variability in the climate and limited data make detecting changes over time far more difficult.

The science of disentangling human and natural influences on our climate is known as attribution. Dr Peter Stott, head of the climate change detection and attribution team at the Met Office and an editor on the report, explained more in a recent  guest blog  for us:

"[The aim is] to compare what actually happened with what might have happened in a world without anthropogenic climate change."

Understanding how our activities are changing the risk of some types of extremes is important for making decisions about how we can prepare for the future.

Hot summers

In summer 2013, western Europe experienced an extreme heatwave. Average temperatures for the June to August period sit just below those of 2003 - the hottest summer in Europe for at least  500 years.

At the same time, the UK experienced its hottest day since 2006 with temperatures of 33.5 degrees Celsius recorded at Heathrow airport, the report notes.

UKheatwave 2014

Sun-seekers flock to Margate in July 2013. Source:   UK heatwave via Shutterstock

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California is in drought, but is climate change to blame?

  • 29 Sep 2014, 15:43
  • Robert McSweeney

California dry ground | Shutterstock

On the 17th January 2014, California's Governor declared a State of Emergency. The drought that had taken hold the year before was showing no signs of abating, with rivers and reservoirs at record lows.

As the situation worsened through 2014, one question was asked again and again - to what extent was human-caused climate change playing a role? A new report out today says the evidence is inconclusive, although it says there are still questions to be explored.

'Ridiculously Resilient Ridge'

Over 95 per cent of California is currently experiencing at least 'severe' drought (shown in orange in the map below), with almost 60 per cent in 'exceptional' drought (deep red).

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Your questions on climate sensitivity answered

  • 26 Sep 2014, 16:00
  • Roz Pidcock

How sensitive is the earth to carbon dioxide? It's a question that's at the heart of climate science.

It's also complicated, and scientists have been grappling with pinning down the exact number for a while now.

But while the exact value of climate sensitivity presents a fascinating and important scientific question, it has little relevance for climate policy while greenhouse emissions stay as high as they are.

Nevertheless, each time a new research paper comes out suggesting climate sensitivity might be low it's misused by parts of the media to argue cutting emissions aren't so urgent after all.

The latest example comes in an  article in today's Times, which claims a new low climate sensitivity estimate means "Climate change could be slower than forecast".

So what is climate sensitivity? What does and doesn't it tell us about future warming?

               Times Climate Sensitivity

Source:  The Times, 26th September 2014

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China tops new list of countries most at risk from coastal flooding

  • 25 Sep 2014, 12:14
  • Robert McSweeney

Ride on flood | Shutterstock

Over 50 million people in China will be at risk from coastal flooding by the end of the century if greenhouse gas emissions continue to stay high, a new study finds.

The research shows Asian countries dominate a top-20 ranking of most vulnerable nations from rising sea levels, with China topping the list.

Interactive map

A team of researchers from the US climate news website Climate Central mapped sea levels around the world using a global database of tide gauge measurements. They then combined these measurements with projections of how much scientists expect sea levels to rise with climate change.

The result is an interactive map, showing the number of people in each country likely to be living with significant risk of flooding by the end of the century. The map can be adjusted for different scenarios of future carbon emissions and sea level rise.

The size of squares shows population at risk, while the colour indicates the proportion of total population at risk.

Climate Central _floodmap

Global estimates of population number (square size) and proportion (square colour) at risk from coastal flooding by 2100 by country. Assumes current emissions trends continue, and a central estimate of sea level rise.   New York Times

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Antarctic sea-ice hits new high as scientists puzzle over the cause

  • 23 Sep 2014, 16:59
  • Robert McSweeney

Broken Ice | Shutterstock

For the third year in a row, the extent of sea-ice around Antarctica has surpassed the previous record high. The extent is now the largest since satellite records began in 1979.

But at the North Pole the decline of Arctic sea-ice continues to accelerate. Scientists haven't yet been able to pin down why the opposite is happening in the Antarctic.

Poles apart

The two poles are very different. The Arctic is a body of water surrounded by land, while the Antarctic is a continent surrounded by water.

It's around this time of year the Antarctic reaches its winter maximum extent and the Arctic reaches its summer minimum .

The latest figures show that at over 20 million square kilometers (sq km), Antarctic sea-ice currently covers a larger area than at any time over the 35-year satellite record.

The blue line on the figure below shows the sea-ice extent for 2014. Typically the annual peak is in September, but it may grow further before the end of the year.

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