CO2 emissions drive heatwaves on despite warming ‘hiatus’

A measurement taken on a shaded back deck in Oswego, Oregon on July 29, 2009 at 6pm. 41.3°C or 106.34°F - just one example of increasingly common hot summers in the Northern Hemisphere. Image copyright  Sean Dreilinger used via Flickr Creative Commons licence.

A measurement taken on a shaded back deck in Oswego, Oregon on July 29, 2009 at 6pm. 41.3°C or 106.34°F – just one example of increasingly common hot summers in the Northern Hemisphere. Image copyright Sean Dreilinger used via Flickr Creative Commons licence.

Human influence on climate is set to make otherwise unusually hot summers in the Northern Hemisphere more frequent, even if the current warming slowdown continues. That finding, from a new study by Youichi Kamae from the National Institute for Environmental Studies in Tsukuba, Japan, and his colleagues, could now heat up climate talks. “The recent hot summers over land regions and the climate hiatus have opposite effects on ongoing global negotiations for climate policies,” Youichi underlined. “The findings of this study can have significant implications for policy makers.”

Over the past 15 years, growing ‘anthropogenic’ or human-emitted CO2 hasn’t turned into significant average temperature rises on the Earth’s surface. The top levels of the oceans haven’t warmed significantly either, even though heat is still building up deeper down. However in that time sometimes deadly hot summers have become more common in Earth’s northern half. It’s not clear how that’s happening without average temperatures increasing faster. One possible part of the explanation could be a fast response to greenhouse gas emissions that Youichi and other scientists had previously found. “The fast response over can largely be interpreted as direct land surface warming due to CO2,” Youichi told me.

The Japanese team’s search for a better explanation had a big question at the centre: How much of this climate change is natural, and how much is man-made? Not able to easily experiment on the planet to investigate, they did what climate scientists usually do for such ‘attribution studies’, and turned to computer models. Simulating the world with and without human greenhouse gas emissions and comparing the results, scientists are increasingly trying to pinpoint whether climate change directly caused particular extreme weather events. They’re trying to build up lots of evidence about a single event to be sure that their result isn’t random, and that takes lots of computer time and power. Read the rest of this entry »

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Unique and unnatural: modern warming from an historical viewpoint

A Roman altar with the Sun in its chariot on the left, and Vulcan, the god of fire and volcanoes on the right. The climate gods long favoured the Roman Empire, with wobbles in Earth's orbit credited for increasing the amount of solar energy falling on Earth at the time. Image copyright: Nick Thompson, used via Flickr Creative Commons License.

A Roman altar with the Sun in its chariot on the left, and Vulcan, the god of fire and volcanoes on the right. The climate gods long favoured the Roman Empire, with Earth’s orbital dance credited for increasing the amount of solar energy falling on Earth at the time. Image copyright: Nick Thompson, used via Flickr Creative Commons License.

Our climate has changed before. It’s something most of us realise and can agree on and, according to Skeptical Science, it’s currently the most used argument against human-caused warming. If such changes have happened naturally before, the argument goes, then surely today’s warming must also be natural. It’s an appealing idea, with an instinctively ‘right’ feel. Nature is so huge compared to us puny humans, how can we alter its course? The warming we’re measuring today must just be a natural fluctuation.

It’s such an appealing argument that at the beginning of the 20th century that’s just what many scientists thought – that humans couldn’t alter Earth’s climate. In the time since, our knowledge has come a long way. We’ve explored space, become able to build the electronics that are letting you read this, and climate science has likewise advanced and benefited from these advances.

So what do we know today that might convince the sceptical scientists of 115 years ago that we’re warming the planet? Recently, Richard Mallett, one of my Twitter friends who describes himself as sceptical about mainstream climate science, made a point that serves as an excellent test of our current knowledge:

Of the historical warmings he’s referring to, perhaps the least familiar is the Holocene, which is ironic, as the Holocene is now. It’s the current period of geological time that started at the end of the last ice age, 11,700 years ago. By 1900 scientists would have known the term, but they couldn’t explain why it wasn’t as icey as before.

Three variables of the Earth’s orbit—eccentricity, obliquity, and precession—affect global climate. Changes in eccentricity (the amount the orbit diverges from a perfect circle) vary the distance of Earth from the Sun. Changes in obliquity (tilt of Earth’s axis) vary the strength of the seasons. Precession (wobble in Earth’s axis) varies the timing of the seasons. For more complete descriptions, read Milutin Milankovitch: Orbital Variations Image credit: NASA/Robert Simmon.

Three variables of the Earth’s orbit—eccentricity, obliquity, and precession—affect global climate. Changes in eccentricity (the amount the orbit diverges from a perfect circle) vary the distance of Earth from the Sun. Changes in obliquity (tilt of Earth’s axis) vary the strength of the seasons. Precession (wobble in Earth’s axis) varies the timing of the seasons. For more complete descriptions, read Milutin Milankovitch: Orbital Variations. Image credit: NASA/Robert Simmon.

The explanation we have today comes thanks to the calculations Milutin Milanković worked out by hand between 1909 and 1941. Milutin showed that thanks to the gravitational pull of the Moon, Jupiter and Saturn, Earth’s orbit around the Sun varies in three ways. Over a cycle of roughly 96,000 years our path varies between more circular and more oval shapes. The other two ways come because Earth’s poles are slightly tilted relative to the Sun’s axis, which is why we have seasons. The angle of that tilt shifts over a roughly 41,000 year cycle. Earth also revolves around that tilted axis, like a spinning top does when it slows down, every 23,000 years.

Together these three cycles change how much of the Sun’s energy falls on and warms the Earth, in regular repeating patterns. Though that idea would be the subject of much controversy, by the 1960s data measured from cylinders of ancient ice and mud would resolve any doubt. The slow descent into ice ages and more abrupt warmings out of them – like the one that ushered in the Holocene – come from Earth’s shimmies in space. Read the rest of this entry »

Climate change science anyone can play with

It’s all very well to read about climate change – but you can probably get a better understanding from actually exploring the data and underlying physics yourself. That’s been driven home by some recent comments on this blog by non-scientist readers wanting to do just this, or recommending that I do. Inspired by them, in this week’s blog entry I’m bringing together various different ways we can all do this. Don’t worry, I won’t tax any weary brain cells any more than they want to be. I’m organising the blog entry in order of increasing effort/difficulty – just bail out or take a break whenever you need to.

The volume occupied by the average yearly CO2 emitted by someone in the UK is as big as a building. Credit: Carbon Quilt

The volume occupied by the average yearly CO2 emitted by someone in the UK is as big as a building. Credit: Carbon Quilt

As a simple starter, try the Carbon Quilt tool that lets you see your CO2 emissions. If you click on this link or the image above you should first see the size of a ‘quilt’ or ‘patch’. That represents the average amount of CO2 people in your country emit, overlaid on a map. Try out the sphere and cube options, and the different options in the drop-down menu to see how big your carbon footprint really is.

Click here to see how hot the Earth's predicted to get in your lifetime, and the lifetimes of children born today. Credit: The Guardian

Click here to see how hot the Earth’s predicted to get in your lifetime, and the lifetimes of children born today. Credit: The Guardian

Another simple but powerful demonstration is the Guardian interactive guide to how warm it will get in our lifetimes pictured above.

Click here to see how unusual current CO2 levels are, and how much worse they're set to get. Credit: The Guardian

Click here to see how unusual current CO2 levels are, and how much worse they’re set to get. Credit: The Guardian

Still more powerful, I think, is this guide showing the significance of CO2 levels in the air hitting 400 parts per million last year. Read the rest of this entry »

Enhanced fingerprinting strengthens evidence for human warming role

Microwave sounding units, like the AMSU units on the Aqua satellite, shown here, can be used to take temperature measurements from different layers in the atmosphere. Ben Santer and his colleagues use this information to find a 'fingerprint' of human impact on recent climate changes. Credit: NASA

Microwave sounding units, like the AMSU units on the Aqua satellite, shown here, can be used to take temperature measurements from different layers in the atmosphere. Ben Santer and his colleagues use this information to find a ‘fingerprint’ of human impact on recent climate changes. Credit: NASA

We have left a clear climate change ‘fingerprint’ in the atmosphere, through CO2 emissions that have made air near the Earth’s surface warmer and caused cooling higher up. That’s according to Ben Santer from Lawrence Livermore National Laboratory (LLNL) in California, who started studying this fingerprint in the mid-1990s, and his expert team. They have strengthened the case by comparing satellite-recorded temperature data against the latest climate models including natural variations within Earth’s climate system, and from the sun and volcanic eruptions. Ben hopes that in the process their results will finally answer ill-tempered criticism his earlier work attracted, and lingering doubts over what causes global warming.

“There are folks out there even today that posit that the entire observed surface warming since 1950 is due to a slight uptick in the Sun’s energy output,” Ben told me. “That’s a testable hypothesis.  In this paper we look at whether changes in the sun plausibly explain the observed changes that we’ve monitored from space since 1979. The very clear answer is that they cannot. Natural influences alone, the sun, volcanoes, internal variability, either individually or in combination, cannot explain this very distinctive pattern of warming.”

That pattern emerged when scientists in the 1960s did some of the first computer modelling experiments looking at what would happen on an Earth with higher CO2 levels in the air. “They got back this very curious warming in the lower atmosphere and cooling of the upper levels of the atmosphere,” Ben explained. The effect happens because most of the gas molecules in the atmosphere, including CO2, sit relatively near to Earth’s surface. CO2’s greenhouse effect lets heat energy from the Sun reach the Earth, but interrupts some of it getting back to the upper atmosphere and outer space. Adding more CO2 by burning fossil fuels therefore warms the lower atmosphere, or troposphere, and cools the stratosphere, 6-30 miles above the Earth’s surface.  Read the rest of this entry »

Deciphering climate messages via the heart of the atom

Vemork Hydroelectric Plant at Rjukan, Norway, which Hans Suess advised on heavy water production, telling Nazi Germany it couldn't make heavy water quickly enough for military use. His expertise with heavy water was part of an interest in nuclear science that led him to become a pioneer in carbon dating.

Vemork Hydroelectric Plant at Rjukan, Norway, which Hans Suess advised on heavy water production, telling Nazi Germany it couldn’t make heavy water quickly enough for military use. His expertise with heavy water was part of an interest in nuclear science that led him to become a pioneer in carbon dating.

When Hans Suess chose to study physical chemistry, he went nuclear, apparently overturning two generations of family tradition. Hans was born in 1909, just as his father Franz succeeded his grandfather Eduard as a geology professor at the University of Vienna. Hans got his PhD from the same university in 1936, but in studying heavy water he was set to aid the historic advances in nuclear science of the time. Yet a transatlantic scientific coincidence would bring him back to more environmental science, and see him help pioneer radiocarbon measurements. With that expertise, Hans showed humans were raising atmospheric CO2 levels, and revealed another surprising source of variations in climate.

The common theme to these achievements was how neutrons and protons combine in an atom’s nucleus. For example, hydrogen atoms found in conventional water have just a single proton in their nuclei. In heavy water, some of these atoms are replaced by a rarer form of hydrogen, known as deuterium, whose atoms have an extra neutron in their nuclei. That gives heavy water properties that can help nuclear reactors, which Nazi Germany notoriously hoped to exploit to make nuclear weapons.

With Hitler’s armies occupying Austria just two years after Hans finished his PhD, his expertise brought him to the attention of the Nazi regime. They called him in to advise a hydroelectric power plant in Vemork, Norway, that was making heavy water. Hans visited several times, reporting that it couldn’t make heavy water quickly enough for military use. Allied forces destroyed it in 1943 anyway, in audacious raids fictionalised in the film “Heroes of Telemark”.

Alongside working with heavy water, Hans studied why the chemical elements exist in the amounts that they do. The answer laid in how stable different numbers of protons and neutrons are when they come together in nuclei. He continued this work after the Second World War in West Germany, helping develop the “Nuclear Shell Theory” explanation, which other scientists won the Nobel Prize for Physics for in 1963. Suess missed out on this acclaim partly because two teams came up with the explanation at the same time. But when the other team, based at the University of Chicago, invited him to visit, Hans’ life changed course towards unravelling the secrets of Earth’s history. Read the rest of this entry »

Google search basis undermines sunspot-winter coldness link

Franck Sirocko's 2012 study incorrectly dated this 1929 postcard identifying a year that the Rhine froze as being from 1963, which is one of many problems Geert Jan van Oldenborgh and his colleagues found with it. Image from van Oldenborgh et al, used under Creative Commons license, see citation below.

Franck Sirocko’s 2012 study incorrectly dated this 1929 postcard identifying a year that the Rhine froze as being from 1963, which is one of many problems Geert Jan van Oldenborgh and his colleagues found with it. Image from van Oldenborgh et al, used under Creative Commons license, see citation below.

European researchers have strongly criticised a recent study linking cold winters in the continent to cycles affecting the sun for relying on a shallow internet search. In August 2012, Franck Sirocko at University of Mainz, Germany, and his teammates linked cold years to sunspot activity lows using historical reports of when the river Rhine froze. But their results disagree with previous research, and previously unpublished findings from Geert Jan van Oldenborgh from KNMI, the Royal Netherlands Meteorological Institute, in De Bilt. And when Geert Jan looked into why this was, he found problems common in research on this topic over 50 years ago, updated for the internet age.

“These problems are fundamental – all the results that they claimed are spurious,” Geert Jan told me. “It is simply an incorrect paper. Usually incorrect results are just ignored, they do not get cited much and are quickly forgotten. However, this time we took the unusual step to write a comment on the paper. This decision was based on the low quality and the wide publicity it was given.”

That publicity came largely because the American Geophysical Union, which published the 2012 paper, put out a press release about it that the media reported widely. It tells how Franck’s team used historical documents to find that the Rhine froze in multiple places fourteen different times between 1780 and 1963. 10 of the 14 freeze years occurred close to the point in an 11 year cycle when there are fewest sunspots. “We provide, for the first time, statistically robust evidence that the succession of cold winters during the last 230 years in Central Europe has a common cause,” Franck said in the press release.

Sunspot cycles had been linked to weather throughout the 19th and 20th centuries, until Barrie Pittock started going over the evidence in the 1970s. Barrie, who led the Climate Impact Group at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia until his retirement in 1999, found no link beyond day-to-day weather effects. He also found many studies had used bad or incomplete data to say otherwise. Read the rest of this entry »

Butterfly effect limits climate models

National Center for Atmospheric Research's Clara Deser. Credit: NCAR

National Center for Atmospheric Research’s Clara Deser. Credit: NCAR

Natural chaos in our climate system creates uncertainty in predictions that can’t be removed, no matter how good scientists’ models get. Clara Deser from the US National Center for Atmospheric Research (NCAR) in Boulder, Colorado and her colleagues have shown these effects can be as strong as human-caused warming. “Over multiple decades intrinsic climate variability on a local and regional scale can be on a par with climate change due to greenhouse gas emissions,” she told me. “You’re not going to just see the result of the greenhouse gas increases – you’re going to see both. This simple message has been missing from the climate change literature.”

Climate scientists are working hard to improve the accuracy of their models’ predictions – perhaps so hard they haven’t yet looked at what their limits are. “We’ve been focussed on identifying how greenhouse gas changes and the like can affect the climate system,” Clara said.  “The uncertainties in climate projections have all been lumped together. There hasn’t been a set of runs that were designed the way that we have done them to really address this point.”

Anyone who’s had to run outside to rescue drying clothes from a rain shower knows that weather can be variable from day to day. Climate patterns also vary from year-to-year, like El Niño or the North Atlantic Oscillation, and some chaotic climate processes work over decades. Wanting to reduce model uncertainty, Clara previously tried to answer a series of detailed questions about these kinds of natural variability. Her team’s answers showed that they accounted for at least half of the disagreement between different climate model predictions. When she told this to two fellow climate scientists, Reto Knutti, from the Swiss Federal Institute of Technology, Zurich and Massachusetts Institute of Technology’s Susan Solomon, they were surprised. “They said, ‘Something very simple and illustrative is needed to get this important message across,’” Clara recalled.
Read the rest of this entry »