Did the Montreal Protocol contribute to the surface warming slowdown?

  • 10 Nov 2013, 21:00
  • Freya Roberts

A ban on gases that created a hole in the ozone layer may have contributed to the slowdown in surface warming, if new research is right. An international team of scientists says that cuts in CFC gases agreed under the Montreal Protocol lowered surface temperatures since the 1990s.

CFCs and the slowdown

A few decades ago chlorofluorocarbons (CFCs) were found in everyday objects like fridges and plastic packaging. That was until scientists discovered the gases were causing a hole in the ozone layer. In 1987 countries from around the world signed the  Montreal Protocol, an international agreement to phase out CFCs.

According to a new study in the journal Nature Geoscience, the international agreement had an unintended consequence for earth's climate. The authors of the study spotted it when looking at the links between the rate of global warming and the speed at which greenhouse gas emissions were increasing.

Their analysis showed that emissions and temperatures had been rising and falling in sync since 1880. In the 1960s there was a jump in both emissions and warming, marking the start of a period of more sustained global warming. Then in the 1990s that warming slowed.

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Natural aerosols complicate climate understanding

  • 06 Nov 2013, 18:15
  • Freya Roberts

Sourced under creative commons

The planet is warming 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 a cooling effect. The big puzzle for scientists is trying to understand how big that effect is.

The tiny particles called aerosols cause clouds to reflect more of the sun's energy back out to space. Human activities add aerosols to the atmosphere, and that spares the Earth's surface some warming. But precisely how much is unknown.

A new study out today offers one reason why it's hard to pin down the size of aerosols' cooling effect. According to Professor Ken Carslaw from the University of Leeds, the problem is not knowing how much natural aerosols were affecting the climate before humans came along and started adding more to the atmosphere. Without a baseline, its hard to measure how much things have changed since.

What are aerosols?

Aerosols are microscopic particles that float in the atmosphere. They come in a range of sizes - the smallest are a few nanometers wide, smaller than the smallest viruses. Larger aerosols can be as big as the diameter of a human hair.

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Solar Activity and the so-called “Little Ice Age”

  • 01 Nov 2013, 12:55
  • Professor Mike Lockwood

I'm a professor of space environment physics and a director of research at the University of Reading in the UK. My particular topic of research is the sun, how it changes over time and how those changes affect the space environment, the weather and the climate on Earth.

In the last few years, my work has focused on how temperatures in the northern hemisphere have responded to periods in history when the sun has been very quiet. The "activity" of the sun's magnetic field is related to the number of sunspots that appear on its surface.

The sun's activity rises and falls on an approximately 11-year cycle, but also varies on century-long timescales. It's this research I talked to BBC weatherman Paul Hudson about in an  interview for the BBC's Inside Out programme.

Unfortunately, I now find myself in the position of being  cited as predicting that the current rapid decline in solar activity will plunge the world into a "Little Ice Age".

This is very disappointing as it is not at all supported by the science. 

Weather and climate are inherently complicated - and uncovering and attributing past changes is very difficult. So it's worth being clear about the state of the science, as well as some of the myths, misconceptions and misnomers that abound in this area.

The "Little Ice Age" wasn't really an ice age

Let us start with the term "Little Ice Age". I personally dislike it and avoid using it, as I don't think it was an ice age of any shape or form.  

There is some evidence for a prolonged period of somewhat lower global mean temperatures beginning in around 1400 -1500 (estimates vary) and ending sometime between 1700 and 1800. 

This has been termed the " Little Ice Age" and is often wrongly linked with the Maunder minimum in solar activity, a period between about 1650 and 1700 when almost no sunspots were seen.

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10,000 year record shows Pacific depths warming fast

  • 31 Oct 2013, 18:45
  • Freya Roberts

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A temperature record built from the shells of tiny sea creatures suggests the middle depths of the Pacific ocean have warmed 15 times faster in the last 60 years than at any time over the last 10,000 years.

Fast-paced warming

By analysing the chemical composition of fossilised sea creatures called foraminifera, the authors of a new study in the journal Science have reconstructed a record of Pacific ocean temperatures stretching back over the past 10,000 years.

Scientists can glean information about what the climate was like at the time the sea creatures were alive. The warmer the water, the more magnesium the shells contain relative to the amount of calcium.

The reconstructed temperature record suggests that for most of the past 10,000 years, water 450 to 1000 metres deep in the Pacific ocean was cooling.

As the graph below shows, there were some ups and downs - the reconstruction suggests that this bit of the ocean was comparatively warmer during the  Medieval Warm Period, about a thousand years ago. It also suggests that the ocean cooled faster during a period referred to as the  Little Ice Age, which followed a few hundred years later.

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Climate scientists don’t think we’re heading for another "Little Ice Age"

  • 29 Oct 2013, 17:00
  • Roz Pidcock

From time to time, we're told by parts of the media that earth is headed for another 'little ice age'. Today was the turn of The Daily Express, in an  article urging us to "get ready" for erratic and extreme weather in the UK.

The paper claims experts warn Britain "faces a new mini-Ice Age with decades of severe Siberian winters and washout summers". But the scientist the paper cites tells us he feels "very misrepresented".

Inside out

The piece is loosely based on comments made by Professor Mike Lockwood from the University of Reading to BBC weatherman Paul Hudson for last night's  Inside Out programme.

The BBC programme looks back over recent cold winters in the UK and opens with the claim, "Scientists are warning that we could be heading towards a mini-ice age".

Hudson wrote up his take on the interview  here, beginning:

"It's known by climatologists as the 'Little Ice Age', a period in the 1600s when harsh winters across the UK and Europe were often severe. The severe cold went hand in hand with an exceptionally inactive sun, and was called the Maunder solar minimum.

Now a leading scientist from Reading University has told me that the current rate of decline in solar activity is such that there's a real risk of seeing a return of such conditions."

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Wet UK summers: melting Arctic sea ice may be partly to blame

  • 29 Oct 2013, 07:50
  • Freya Roberts and Roz Pidcock

Between 2007 and 2012, northern Europe experienced a run of wetter than average summers. In England, the summer of 2012 was the wettest for 100 years. Now a new study says rapidly diminishing Arctic sea ice may be partly responsible.

In the last few years, scientists looking into the consequences of melting Arctic sea ice have suggested a link to  colder winters in the UK.

The new study, just published in the journal Environmental Research Letters, is the first to find evidence that changes at the North Pole may be affecting our summer weather too.

Soggy summers

For six consecutive summers, northern Europe experienced unusually wet weather. The amount of rain that fell each year was higher than average, but having such a long run of wet summers is what really surprised scientists.

Dr. James Screen, author of the new study and research fellow at the University of Exeter, tells us:

"Taken together the six summers 2007 to 2012 were around 15 to 25 per cent wetter than average over much of Northern Europe."

In England and Wales, the summer of 2012 was the wettest since 1912. The summer of 2007 was the second wettest. Screen adds:

"During the wettest summer, 2012, northern Europe experienced 80% more rainfall than normal."

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Eight years' worth of current emissions halves the chances of staying below two degrees warming

  • 23 Oct 2013, 14:15
  • Roz Pidcock

Limiting global warming to two degrees above pre-industrial levels will require "substantial and sustained" cuts in greenhouse gas emissions, the Intergovernmental Panel on Climate Change (IPCC) said in its latest  report.

It went a step further by proposing a "carbon budget" - a first for the IPCC reports. This is a total amount of carbon we can put into the atmosphere while still having a good chance of staying below the critical two degree threshold.

How scientists work out the budget is quite complicated - we have written a more detailed briefing  here. But here are the most important bits.

Two thirds of the budget is already spent

According to the IPCC's calculations, 800 billion tonnes is the maximum amount of carbon we can release through carbon dioxide emissions to still have a 66 per cent chance of limiting warming to two degrees - a probability the IPCC terms "likely".

This budget allows for some additional warming to come from emissions other than carbon dioxide, including methane, CFCs, ozone, nitrous oxide and black carbon.

Carbon dioxide emissions over the industrial era have put about 531 billion tonnes of carbon into the atmosphere - which means we've already 'spent' about two thirds of the budget.

If emissions were to continue at current levels, the remaining budget - about 270 billion tonnes - would be exhausted in about 25 years.

To stay within budget, any fossil fuels that would put us over budget would have to be left in the ground - or the emissions  captured before or after entering the atmosphere.

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Carbon briefing: Making sense of the IPCC’s new carbon budget

  • 23 Oct 2013, 10:00
  • Roz Pidcock

Last month, the Intergovernmental Panel on Climate Change (IPCC) released its fifth 'assessment report', which provide a detailed look at the science of climate change.

The latest report  is the first to include an assessment of a "carbon budget" - a finite amount of carbon that can be burnt before it becomes unlikely we can avoid more than two degrees of global warming.

So how big is the carbon budget, how was it calculated, and how does it help us understand the challenge of limiting climate change?

A budget for two degrees

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

The most widely accepted threshold is two degrees of warming relative to pre-industrial times - this is the limit recommended by the UK's  Committee on Climate Change, for example.

In its new report, the IPCC includes a calculation of how much carbon we can emit and still have a reasonable chance of staying below two degrees.

It calls this amount a carbon budget. The budget is an upper limit on total human emissions, from the beginning of the industrial revolution until the day we stop burning carbon.

To stick to the budget, any fossil fuels that would take us over-budget will either have to be left in the ground, or the emissions  captured before or after entering the atmosphere.

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Drying in the Amazon rainforest - what could it mean for climate change?

  • 22 Oct 2013, 17:00
  • Freya Roberts

CC - Cajie on Flickr

The southern reaches of the Amazon rainforest are drying up - a little bit more each year. That's according to a new study which finds that since 1979, the region's dry season has got about a week longer each decade.

If these outer edges of the rainforest spend too much time each year exposed to dry conditions, they could be prone to more forest fires and could ultimately end up changing into an entirely different habitat - one that locks up much less carbon dioxide.

Even a partial loss of rainforest would substantially increase carbon levels in the atmosphere, say the authors, with consequences for the climate.

Longer dry seasons

The new research shows that since 1979, the dry season in southern parts of the Amazon rainforest has grown by about seven days per decade. The authors can't definitively link the changes to any one factor, but say the trend they observed resembles the effects of climate change.

Overall, scientists know rainforests are  resilient to some level of climate change. But a longer dry season is particularly problematic for trees in areas where conditions are only just wet enough for rainforest species to survive. Like on the southern edge of the Amazon, for example.

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No corner of the ocean will escape climate change, say scientists

  • 18 Oct 2013, 14:30
  • Freya Roberts

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Humans' greenhouse gas emissions are changing the oceans' chemical makeup - posing risks to wildlife and coastal communities. That's the conclusion of a  new study which says every part of the ocean's surface will feel the effects of climate change by the end of the century.

Last month the IPCC's major climate science report warned the oceans were already warming, becoming more acidic and less productive - changes an international team of ocean scientists have described as a " deadly ocean trio".

Chemical changes

Probably the best-known effect of climate change on the oceans is sea level rise. But scientists are tracking a variety of ways that the oceans are changing.

As a result of humans' rising carbon emissions, the oceans are also warming. The Intergovernmental Panel on Climate Change (IPCC) estimates that since the 1970s, oceans have taken up more than  90 per cent of the heat trapped by greenhouse gases. Temperatures have risen both at the surface and in the deep ocean.

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