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 »

Who can afford to hold back rising seas?

UK Prime Minister David Cameron visiting Dawlish a week after the storms that demolished the sea wall that supported the train line. Image copyright Number 10, used via Flickr Creative Commons license.

UK Prime Minister David Cameron visiting Dawlish a week after the storms that demolished the sea wall that supported the train line. Image copyright Number 10, used via Flickr Creative Commons license.

Taking the train along the Devon, UK, coast earlier this week I was hypnotised by the lapping waves I saw through the window, and their concealed power. On such a sunny day, the rail journey through Dawlish is perhaps the most beautiful I’ve been on. But in February its ocean-hugging route became its downfall, when storms demolished the sea wall it rests on. Now, thanks to 300 fluorescent-jacket clad workers who performed £35 million worth of repairs, the dangling tracks I saw on TV news are a fading memory. It’s an impressive achievement, but could we afford it if – due to climate change, for example – such ‘orange armies’ had to do battle more often?

The significance of that question was emphasised by Chris Field from Stanford University in California, when I saw him talk recently. Highlighting that all parts of the world are vulnerable to climate change, Chris showed the below image of New York City in 2011, during Hurricane Sandy. “The existing climate created a situation that caused over $50 billion in economic damage for a region of the world that had a vast amount of economic resources and had a response plan in place,” he underlined. “It just wasn’t a plan that was up to the challenges that they faced.” If climate change causes more $50 billion-damage events, can we afford that?

If New York can be taken unaware by Hurricane Sandy, what happens elsewhere, when sea level's higher? Image credit: Chris Field/IPCC

If New York can be taken unaware by Hurricane Sandy, what happens elsewhere, when sea level’s higher? Image credit: Chris Field/IPCC

Just before the ocean crippled the south-west UK’s rail services, Jochen Hinkel from the Global Climate Forum in Berlin, Germany, and his team were answering a similar question. In a paper published in the Proceedings of the National Academy of Sciences of the USA in February, Jochen looked at coastal flood damages from projected sea level rise. When I therefore asked him about his work, he was quick to put climate change-driven sea level rise’s role in Hurricane Sandy and this year’s UK storms into context. Read the rest of this entry »

IPCC: Millions of words on climate change are not enough

The latest IPCC report has highlighted that it's dead certain that the world has warmed, and that it's extremely likely that humans are the main cause. Credit: IPCC

The latest IPCC report has highlighted that it’s dead certain that the world has warmed, and that it’s extremely likely that humans are the main cause. Credit: IPCC

The most recent UN Intergovernmental Panel on Climate Change (IPCC) report saw perhaps the most severe conflict between scientists and politicians in the organisation’s existence. As its name suggests, governments take an active part in the IPCC process, whose latest main findings appeared between September 2013 and May 2014. Debate over what information makes the high-profile ‘Summaries for Policymakers’ is usually intense, but this time three graphs were dropped on politicians’ insistence. I show these graphs later in this blog entry.

At the Transformational Climate Science conference in my home town, Exeter, UK, earlier this month, senior IPCC author Ottmar Edenhofer discussed the ‘battle’ with governments on his part of the report. Another scientist who worked on the report highlighted confidentially to me how unusual the omission was.

To me, it’s more surprising that this hasn’t happened more often, especially when you look more closely at the latest report’s findings. There’s concrete certainty that warming is happening, and it’s extremely likely that humans are the dominant cause, it says. Governments have even – in some cases, begrudgingly – already signed up to temperature and CO2 emission targets reflecting this fact.

The inadequacy of those words is becoming ever more starkly obvious. Ottmar stressed that the emissions levels agreed at the United Nations’ Climate Change Conference in Cancún, Mexico, in November 2010, would likely need later emissions cuts the likes of which we’ve never seen before to avoid dangerous climate change. The latest IPCC report shines a floodlight on that inertia, which understandably cranks up the tension between researchers and politicians.

Ottmar was one of two co-chairs who led the ‘working group three’ (WGIII) section of the IPCC report that looks at how to cut greenhouse gas emissions. He stressed that the need to make these cuts comes from a fundamental difference between the risks that come from climate change and the risks of mitigation. We can heal economic damage arising from cutting emissions – reversing sea level rise isn’t so easy.

Read the rest of this entry »

Real-world grounding could cool 21st century outlook

The world's surface air temperature change ("anomaly"), relative to the world's mean temperature of 58° F or 14.5° C, averaged over land and oceans from 1975 to 2008. Inset are two periods of no warming or cooling within this overall warming trend. Copyright 2009 American Geophysical Union. Reproduced/modified by permission of American Geophysical Union.

The world’s surface air temperature change (“anomaly”), relative to the world’s mean temperature of 58° F or 14.5° C, averaged over land and oceans from 1975 to 2008. Inset are two periods of no warming or cooling within this overall warming trend. Copyright 2009 American Geophysical Union. Reproduced/modified by permission of Wiley/American Geophysical Union, see citation below.

Starting climate models from measured data helps simulate the early-2000s global warming hiatus better, and reduces projections for warming through to 2035. Jerry Meehl and Haiyan Teng have compared such ‘initialised’ model runs against more common ‘uninitialised’ ones starting without real-life conditions. The scientists, from the US National Centre for Atmospheric Research (NCAR) in Boulder, Colorado, find initialised runs get closer to modelling that hiatus and surprisingly rapid warming in the 1970s. Using the same approach, admittedly rough 30-year predictions for Earth’s surface air temperature initialised in 2006 are about one-sixth less than uninitialised projections. “We have evidence that if we would have had this methodology in the 1990s, we could have predicted the early-2000s hiatus,” Jerry told me.

The hiatus Jerry and Haiyan studied – an easing off in the rate of global warming since 1998 – is perhaps the aspect of climate change most hotly debated today. But hiatus is a slippery word, whose meaning depends on who is highlighting what points on which graph. Climate skeptics will often infer that it’s evidence that global warming is not a problem, or that it shows we know too little to act on climate change. The UN Intergovernmental Panel on Climate Change puts it in plain numbers: the rate of warming from 1998-2012 was 0.05°C per decade; from 1951 to 2012, it was 0.12°C per decade. “In addition to robust multi-decadal warming, global mean surface temperature exhibits substantial decadal and interannual variability,” it adds.  “Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.”

In a paper published online in the journal Geophysical Research Letters last week, Jerry and Haiyan touch on the current best explanations of the let-up. These include the chilling effect of recent volcano eruptions, but mostly focus on cooling in the Pacific as part of a natural cycle. Called the Interdecadal Pacific Oscillation (IPO), this regular wobble in sea surface temperatures has likely partly masked greenhouse-gas driven warming. The IPO has also been linked to a larger warming than might have been expected from greenhouse gases alone in the 1970s, the NCAR researchers add. Read the rest of this entry »

Fighting for useful climate models

  • This is part two of a two-part post. Read part one here.
Princeton University's Suki Manabe published his latest paper in March this year, 58 years after his first one. Credit: Princeton University

Princeton University’s Suki Manabe published his latest paper in March this year, 58 years after his first one. Credit: Princeton University

When Princeton University’s Syukuro Manabe first studied global warming with general circulation models (GCMs), few other researchers approved. It was the 1970s, computing power was scarce, and the GCMs had grown out of mathematical weather forecasting to become the most complex models available. “Most people thought that it was premature to use a GCM,” ‘Suki’ Manabe told interviewer Paul Edwards in 1998. But over following decades Suki would exploit GCMs widely to examine climate changes ancient and modern, helping make them the vital research tool they are today.

In the 1970s, the world’s weather and climate scientists were building international research links, meeting up to share the latest knowledge and plan their next experiments. Suki’s computer modelling work at Princeton’s Geophysical Fluid Dynamics Laboratory (GFDL) had made his mark on this community, including two notably big steps. He had used dramatically simplified GCMs to simulate the greenhouse effect for the first time, and developed the first such models linking the atmosphere and ocean. And when pioneering climate research organiser Bert Bolin invited Suki to a meeting in Stockholm, Sweden, in 1974, he had already brought these successes together.

Suki and his GFDL teammate Richard Weatherald had worked out how to push their global warming study onto whole world-scale ocean-coupled GCMs. They could now consider geographical differences and indirect effects, for example those due to changes of the distribution of snow and sea ice. Though the oceans in the world they simulated resembled a swamp, shallow and unmoving, they got a reasonably realistic picture of the difference between land and sea temperatures. Their model predicted the Earth’s surface would warm 2.9°C if the amount of CO2 in the air doubled, a figure known as climate sensitivity. That’s right in the middle of today’s very latest 1.5-4.5°C range estimate.

Comparison between the measured sea surface temperature in degrees C calculated by the GFDL ocean-coupled GCM, from a 1975 GARP report chapter Suki wrote - see below for reference.

Comparison between the measured sea surface temperature in degrees C calculated by the GFDL ocean-coupled GCM, from a 1975 GARP report chapter Suki wrote – see below for reference.

At the time no-one else had the computer facilities to run this GCM, and so they focussed on simpler models, and fine details within them. Scientists model climate by splitting Earth’s surface into 3D, grids reaching up into the air. They can then calculate what happens inside each cube and how it affects the surrounding cubes. But some processes are too complex or happen on scales that are too small to simulate completely, and must be replaced by ‘parameterisations’ based on measured data. To get his GCMs to work Suki had made some very simple parameterisations, and that was another worry for other scientists. Read the rest of this entry »

The model scientist who fixed the greenhouse effect

Syukuro ("Suki") Manabe in the 1960s at Princeton University, New Jersey, where he taught from 1968-1997. He was working on weather prediction in Tokyo during the difficult postwar years when he was invited to come to the US Weather Bureau's unit working on the general circulation of the atmosphere. He was assigned programmers to write computer code so he could concentrate on the physical concepts and mathematics. Image copyright: AIP Emilio Segrè Visual Archives, used with permission.

Syukuro (“Suki”) Manabe in the 1960s at Princeton University, New Jersey, where he taught from 1968-1997. He was working on weather prediction in Tokyo during the difficult postwar years when he was invited to come to the US Weather Bureau’s unit working on the general circulation of the atmosphere. He was assigned programmers to write computer code so he could concentrate on the physical concepts and mathematics. Image copyright: AIP Emilio Segrè Visual Archives, used with permission.

In 1963, using one of the world’s first transistor-based supercomputers, Syukuro Manabe was supposed to be simulating how Earth’s atmosphere behaves in more detail than ever before. Instead, the young US Weather Bureau scientist felt the frustration, far more common today, of a crashed system. But resolving that problem would lead ‘Suki’ Manabe to produce the first computerised greenhouse effect simulations, and lay the foundations for some of today’s most widely used climate models.

After growing up during the Second World War, studying in bomb shelters, Suki entered the University of Tokyo in 1949 to become a doctor like his father and grandfather. The same year Japanese physicist Hideki Yukawa won a Nobel Prize, and helped drive many students into his subject, including Suki. “I gradually realized, ‘Oh my God, I despise biology,’” he told interviewer Paul Edwards in 1998. But to start with, he wasn’t very successful in his new subject. “At the beginning my physics grade was miserable – straight C,” he recalled.

Those grades came about because Suki’s main interest was in the mathematical parts of the subjects, but he hadn’t been thinking about what the maths really meant. When he realised this he concentrated on the physics he found most interesting, in subjects related to the atmosphere and oceans, and his grades started to improve. “By the time I graduated from geophysics and went on to a Master’s course at the University of Tokyo, I was getting a pretty solid way of thinking about the issues,” he said.

Suki went on to get a PhD, but when he finished the kinds of jobs in meteorology he was qualified for were hard to find in Japan. But he had applied his interests to rainfall, in an approach known as numerical weather prediction pioneered by scientists like John von Neumann, Carl-Gustaf Rossby and Bert Bolin. Another leader in the field, Joe Smagorinsky, was looking at rainfall in a similar way, and had read Suki’s research. Joe was setting up a numerical weather prediction team at the US Weather Bureau in Washington, DC, and in 1958 invited Suki to join him.

Their early models split the world into grids reaching into the air and across its surface, calculating what happens within and between each cube as today’s versions still do. But Joe wanted Suki to go further in preparation for the arrival of a transistorised IBM ‘Stretch’ computer in 1963. Joe wanted to develop complex system models that included the role of water movements, the structure of the atmosphere, and heat from the Sun. In particular Joe wanted to push from simulating two layers in the atmosphere to nine. Read the rest of this entry »

Twin rainfall effects strengthen human climate impact case

While existing studies of rainfall changes rely on data collected on land, by switching to satellite data LLNL's Kate Marvel and Céline Bonfils could include changes in rainfall at sea. Image copyright snoboard1010 used via Flickr Creative Commons license.

While existing studies of rainfall changes rely on data collected on land, by switching to satellite data LLNL’s Kate Marvel and Céline Bonfils could include changes in rainfall at sea. Image copyright snoboard1010 used via Flickr Creative Commons license.

The way we humans are affecting the climate is changing rainfall patterns over land and sea, scientists at Lawrence Livermore National Laboratory (LLNL) in California have found. Kate Marvel and Céline Bonfils compared precipitation ‘fingerprints’ in satellite data against what climate models showed would result from actions like adding greenhouse gases to the atmosphere. “Everyone knows that temperatures are rising, but figuring out how that affects other aspects of the climate is tricky,” Kate told me. “We’ve shown that global precipitation is changing in the way climate scientists expect it to. The odds of the observed trends being due to natural climate variability are very low.”

Changes to rain, snow and all the other forms of falling wetness collectively known as precipitation are undeniably important, given their power to bring floods and droughts. Scientists have already shown that, over land, wet areas are getting wetter and dry areas are getting drier. These studies rely on data measured directly on land, reaching back almost a century. The long record gives scientists a lot of data to test, making it easier to tell human influences from the many natural rainfall patterns. Yet Kate and Céline wanted to use satellite data instead. Though these have only been recorded since 1979, each measurement is more reliable, and the satellites also cover the oceans.

“With such a short record, it’s often difficult to identify the ‘signal’ of climate change against the background of completely natural variability,” Kate explained. For example, the wet-gets-wetter, dry-gets-dryer strengthening of the Earth’s water cycle happens because warmer air can hold more water vapour. But that can be caused by the El Niño climate pattern, as well as by increasing greenhouse gases. Our activities can also change how air circulates above the planet, pushing dry regions and storm tracks toward the poles – but so can the La Niña pattern.

Read the rest of this entry »

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