the climate brief Accurate Reporting of Climate Science

Five hundred US-based earth scientists have published a  statement that "science unequivocally demonstrates" humans are affecting the environment through climate change. But although statements of consensus have become commonplace over the past decade, surveys indicate people still believe scientists disagree. So is it really possible to create effective messages about consensus? 

What is scientific consensus? 

Scientific consensus is a measure of where the weight of evidence lies in a particular discipline. In the case of climate change, the weight of evidence indicates that human-produced greenhouse gases are trapping heat in the atmosphere, causing it to warm - and it's a position the vast majority of scientists subscribe to. 

Over the past decade, scholars have  attempted to  measure how strong this consensus in the climate science community is. Most recently, the climate science blog, Skeptical Science, produced a study indicating that of 12,000 papers on climate change 97 per cent of those that expressed a view on the causes of climate change said it was mostly down to human activity - a very similar result to that of previous studies. 

Read more

A new paper suggesting temperatures might not rise as much as some models predict in the near future has been interpreted in some corners - notably by  Matt Ridley in the Times - as a sign that climate change no longer poses a problem. But the authors have spoken out against Ridley's arguments, highlighting why pinpointing earth's sensitivity to greenhouse gases relies on more than one estimate.

The story stems from a  letter in Nature Geoscience on Sunday with a new estimate of what scientists call equilibrium climate sensitivity. That's the total warming we can expect from a doubling of carbon dioxide in the atmosphere, compared with pre-industrial levels.

Climate sensitivity is important because the higher it is, the more warming there will be. In its 2007 report, the Intergovernmental Panel on Climate Change (IPCC) estimated a likely range of between  two and 4.5 degrees Celsius, with a best estimate of three degrees.

More than one way to estimate climate sensitivity

There are different ways to go about calculating climate sensitivity - which is part of the reason the IPCC's range is so large. The new study used what's called an energy budget model, which used land, atmosphere, ice and ocean temperatures between 1970 to 2009 to see how warming in all parts of the climate system has changed in that time. We wrote more about the new paper  here.

Scientists can also use natural recorders of temperature - called  climate proxies - to look at how earth's temperature has changed in response to greenhouse gases throughout its distant past. The third way is using complex climate models to simulate how processes affecting temperature rise are likely to evolve in the future.

Uncertainties about some of these processes - particularly how clouds affect the rate of warming - means climate model estimates can vary quite widely.

Read more

Sourced under creative commons

Monday's tornado in Oklahoma highlights the threat extreme weather poses to human life, and has prompted some to ask if human-caused climate change is partly to blame. Unfortunately, that's a questions scientists still can't answer.

The overwhelming response in the  media and  online in the wake of the tornado has done a pretty good job of accurately reflecting the science, which is so far unclear over whether theres a link between climate change and tornadoes. This statement from scientist Michael Wehner sums up the situation pretty well:

"With tornadoes, what we don't know is as much as what we do know."

Tornadoes 101

Before we dig into the science in more detail, here's a quick introduction to  what tornadoes are and how they form.

Tornadoes are narrow, spinning columns of air reaching from a the base of a thunderstorm down to the ground. They actually only account for a fraction of the energy released in a thunderstorm, but that energy is concentrated on a small area.

Read more

The BBC's Today programme has seven million listeners, so how it covers climate science is quite important. This morning's programme saw a report on climate change and recent temperature rise, followed by an interview with the well-known climate scientist Dr James Hansen.

Broadly speaking, the programme did a good job of navigating what has become an entangled web of scientific issues, although it perhaps inevitably lacked clarity on a few points.

BBC environment correspondent Roger Harrabin posed the question "what kind of risk are we taking with the climate?" With greenhouse gases in the atmosphere rising, earth's surface temperature - that's the air over the land and ocean - has risen more slowly over the past decade and a half than in previous decades.

The Today programme report explored why this might be, while Dr Hansen was on hand to explain why despite the recent slow pace of surface warming, the science of climate change isn't really in doubt.

Read more

Research suggests  support for climate change action increases if the public is aware of a scientific consensus on the evidence for human causes. But how many scientists really agree? A new  study, out today, shows very few studies reject that climate change is human caused, and hopes to promote this message by encouraging the public to get involved. 

A team of volunteers from climate science blog, Skeptical Science, rated the abstracts of nearly 12,000 peer-reviewed papers based on their level of agreement that climate change is human caused. The new study aims to identify the level of consensus by analysing 20 years of climate change literature.  

Read more

From Tuvalu to Alaska, some communities are already feeling the effects of rising sea levels - but knowing just how much melting ice is contributing to sea level rise, and what we can expect in the future is more difficult. A major EU project has just released new projections - and it says sea levels could rise nearly 70 cm by 2100.

Today's media have reported the new projections but seem confused over whether they're better or worse than expected. The Times says the risk from rising seas is "worse than feared", whereas the  New Scientist claims "it's not as bad as we thought".

As it turns out it could be seen as a bit of both - here's why.

Ice2sea

Four years ago, the Ice2sea project launched with the aim of improving scientists' projections of how much melting sea ice will contribute to global sea level rise.

Two years previously, the  IPCC 4th assessment report gave a best estimate of sea level rise of around 40 cm by 2100, but said the biggest uncertainty was the contribution to sea level rise from ice sheets and glaciers.

As ice sheets and glaciers melt, water that was previously held on land is added to the ocean, causing sea levels to rise. Head of the Ice2sea project, Professor David Vaughan of the British Antarctic Survey, explained at the launch of the project's final report last night:

Read more

For more than a hundred years, scientists have known greenhouse gases warm the atmosphere. But despite trapping more and more heat, earth's surface temperature over the past decade and a half has risen slowly. And understanding where the extra heat ends up can be more complicated. 

We talk to Dr Richard Allan, lead researcher on a new project called Deep-C, about how the tools to take earth's temperature have changed - and how new measurements can help scientists investigate what's behind the surface warming slowdown.

Allan is a climate science researcher at the University of Reading's department of meteorology. His career has focussed on combining measurements with climate models to understand changes in earth's climate.

Heat sink

When we talk about the earth's temperature, we usually mean the temperature of the air above the land and ocean, or surface temperature, as it's what humans experience most directly. But surface temperature is only a small part of the climate system. In fact, most of the extra heat the planet absorbs goes into the oceans. Allan tells us:

"The vast ocean has a huge capacity to store heat … There's a very good relationship between the extra radiative energy entering the top of Earth's atmosphere - due to increases in greenhouse gases - and ocean heating."

Read more

The Arctic wasn't always as cold and icy as it is now. Three million years ago, carbon dioxide levels were similar to today - but summer temperatures were eight degrees Celsius higher and Greenland was almost ice-free. A new study has scientists speculating whether earth's distant past can provide a window into future climate change.

Ancient lake

Scientists can glean clues about the history of Earth's climate by examining plants and animals preserved in ancient sediments. Fossilised pollen can reveal the vegetation that existed at different times, which in turn paints a picture of temperature and rainfall.

Published today in the journal Science, a new study uses the longest sediment core ever collected from the Arctic to reconstruct polar temperature between 2.2 and 3.3 million years ago.

The international team of scientists analysed fossilised pollen from layers of sediment below an 18 kilometre-wide lake in the northeast Russian Arctic, which formed when a meteorite hit earth nearly 3.6 million years ago.

Read more

Horst Machguth

A new study estimates how much Greenland's glaciers could raise sea level under a warming climate - and it could be as much as 8.5 cm by 2100. This is less than some previous models suggest, but not insignificant for calculating total sea level rise.

Satellite data suggests that over the last 20 years, the Greenland ice sheet has lost  140 billion tonnes of ice each year. As ice sheets melt, water that was previously held on land is added to the ocean, causing sea levels to rise.

As well as warmer air directly melting the  surface of the ice sheet, glaciers are an important part of the picture. Glaciers move ice from the ice sheet to the sea, and  react quickly to changes in atmospheric conditions.

This sensitivity makes glaciers very visible indicators of climate change. But unravelling the different ways they're affected by rising temperature has proven challenging, which means the contribution of Greenland's glaciers to sea level rise is not well understood.

Read more

Despite greenhouse gas emissions continuing to rise fairly steadily, earth's surface - that's the land and top of the oceans - has warmed relatively slowly over the past fifteen years or so.

We asked climate scientists to give us their thoughts about what's causing the recent slower pace of surface warming. Here's what they told us.

Recent slower warming isn't unusual

To draw conclusions about climate change, climate scientists tend to look at long time periods - temperatures measured over decades, or whole centuries. The last 15 years or so is a relatively short amount of time to measure temperatures over.

There are good reasons for taking a longer view. As professor  Gabriele Hegerl from the University of Edinburgh tells us, surface temperatures bounce around from one year to the next because of natural fluctuations in the climate:

"Climate change becomes more visible against [natural fluctuations when] the longer periods are considered ... To see the long-term change, long periods need to be considered, such as multiple decades."

Read more