2010 Diary week 39
Global warming, climate change and weather extremes
Book Review
Below you will find the review of Part VII of With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change by Fred Pearce. These are some snippets: “El Niňo is a periodic reversal of ocean currents, winds, and weather systems that stretches across the equatorial Pacific Ocean, halfway around the planet at its widest girth. It is a redistributor of heat and energy in the hottest part of the world’s oceans, which kicks in when the regular circulation systems can no longer cope.” “Deprived of their storm-generating weather systems, Indonesia and a wide area of the western Pacific, including much of Australia, dry out. There are forest and bush fires, and crops shrivel in the fields.” “In 1998 Donald Rodbell, of Union College, in Schenectady, New York published a 12,000-year record of the floods of a lake in southern Ecuador. For the first half of the period, they came roughly once every 15 years, suggesting a near-dormant El Niňo.” “Publishing his findings Schrag said: “In 1982-83 we experience the most severe El Niňo of the 20th century. According to previous records you wouldn’t expect another that powerful for a hundred years. But 15 years later, in 1997-98, we have one even larger.” “What is becoming clear is that El Niňo is a phenomenon that influences basic planetary processes such as the transfer of heat and moisture in huge swaths of the tropics. That it has big swings that operate on timescales varying from months to thousands of years. That it leaves its calling card in different ways right around the planet. And that its variability seems to be keyed into critical external drivers of past climate such as the precession and Bond’s 1,500-year solar cycles.”
WITH SPEED AND VIOLENCE
WHY SCIENTISTS FEAR TIPPING POINTS IN CLIMATE CHANGE
FRED PEARCE
BEACON PRESS 2007
PART VII
Chapter 30: A Chunk of Coral
• Back in the lab at Harvard, Dan Schrag discovered that this fossilized piece of coral was 125,000 years old and contained 65 years’ worth of growth rings, the first piece ever located that was large enough and well enough preserved to give a good snapshot of ancient El Niňos.
• El Niňo is a periodic reversal of ocean currents, winds, and weather systems that stretches across the equatorial Pacific Ocean, halfway around the planet at its widest girth. It is a redistributor of heat and energy in the hottest part of the world’s oceans, which kicks in when the regular circulation systems can no longer cope.
• In normal times, the winds and surface waters of the tropical Pacific, driven by Earth’s rotation, flow from the Americas in the East to Indonesia in the West. In the tropical heat, the water warms as it goes. The result is the gradual accumulation of a pool of hot water on the ocean surface around Indonesia.
• This pool can be up to 13°F warmer than the water on the other side of the ocean, and can contain more heat energy than the entire atmosphere. All that heat generates storm clouds that keep the rainforests of Southeast Asia wet.
• The constant flow to the west piles up water. Trapped against the Indonesian archipelago, the warm pool can rise as much as 15 inches above sea levels farther east.
• Every few years, usually when winds slacken, this raised pool of warm water breaks out and flows back across the surface of the ocean, right along the equator. As the warm water moves east, the wind and weather systems that it creates follow.
• Deprived of their storm-generating weather systems, Indonesia and a wide area of the western Pacific, including much of Australia, dry out. There are forest and bush fires, and crops shrivel in the fields.
• The displaced wet and stormy rainforest climate drenches normally arid Pacific islands, and often reaches the coastal deserts of the Americas. Ripples from this vast movement of heat and moisture spread around the globe.
• Typically, an individual El Niňo event lasts 12 to 18 months. After it has abated, the system often goes into sharp reverse, with exceptionally wet conditions in Indonesia and fierce drought further east. This is called La Niňa.
• Together, El Niňo and its sister constitute a vast oscillation of ocean and atmosphere that in recent times has been the most intense fluctuation in the world’s climate system.
• Reliable climate and ocean records cover only a couple of centuries or so. Delving further requires alternative sources of information.
• In 1998 Donald Rodbell, of Union College, in Schenectady, New York published a 12,000-year record of the floods of a lake in southern Ecuador. For the first half of the period, they came roughly once every 15 years, suggesting a near-dormant El Niňo.
• Then they speeded up quite abruptly, to settle at an average return period of about 6 years – the classic El Niňo pattern until recently. This pattern has been confirmed by Lonnie Thompson’s ice cores from nearby glaciers.
• The change in the flood pattern also seems to coincide with the same precession shift in Earth’s tilt that caused the desertification of the Sahara and the advance of tropical glaciers spotted by Thompson.
• When water evaporates, molecules containing the lighter isotope of oxygen – oxygen-16 – evaporate slightly faster, leaving behind seawater that is rich in the heavier oxygen-18.
• Schrag measured the ratio of the two oxygen isotopes in the 65 annual growth rings in his ancient chunk of coral, finding two things of importance.
• First there had indeed been an El Niňo cycle back then. Second, the El Niňo cycle looked exactly like that of the modern period from the mid-1800s to the mid-1970s, in which El Niňo returned, on average, about every 6 years.
• This underlined the idea that 6 years is the natural length of the cycle – and made the post 1976 period, during which El Niňo has developed a return period averaging 3.5 years, appear increasingly unusual.
• Publishing his findings Schrag said: “In 1982-83 we experience the most severe El Niňo of the 20th century. According to previous records you wouldn’t expect another that powerful for a hundred years. But 15 years later, in 1997-98, w have one even larger.”
• And since then, in 2002 and 2004, there have been two more significant El Niňos – not as large as those before, but turning up with ever-greater frequency.
• What is becoming clear is that El Niňo is a phenomenon that influences basic planetary processes such as the transfer of heat and moisture in huge swaths of the tropics. That it has big swings that operate on timescales varying from months to thousands of years. That it leaves its calling card in different ways right around the planet. And that its variability seems to be keyed into critical external drivers of past climate such as the precession and Bond’s 1,500-year solar cycles.
Chapter 31: Feeding Asia. What happens if the monsoon falters?
• More than 3 billion people today are fed and watered thanks to the Asian monsoon. It is the greatest rainmaking machine on the planet – and possibly one of the most sensitive to climate change.
• A failed monsoon has devastating consequences. British colonial administrators in India watched in bemusement as tens of millions died in the famine of 1837-38, and again in 1860-1861, 1876-1878, and 1896-1902.
• The rains proved more reliable in the 20th century than in the 19th and has appeared to be self-contained and invulnerable. If the monsoon proves less reliable in the 21st century, there could be real trouble ahead – for about 3 billion people.
• Strong El Niňos often seem to switch off the Asian monsoon. If the Pacific climate system does what many predict, and in the 21st century leans heavily towards a permanent El Niňo-like state, and if the monsoon resumes its former relationship, then the rains may soon fail over Asia more often than they succeed.
• In 2003 Indian and U.S. researchers assembled a 10,000-year record of the strength of the Indian monsoon by counting fossilized plankton found in ancient marine sediments off the Indian coast, finding a huge variability in the monsoon’s strength over the centuries. Strong monsoons go hand in hand with warm waters off Europe and North America.
• Changes clearly followed Bond’s 1,500-year solar pulse. Jonathan Overpeck, of the University of Arizona, says that a warm North Atlantic sends heat east on the winds, warming Asia in the spring, and allowing a rapid melt of the Tibetan plateau and an early start to the rain-giving monsoon winds.
• When the Atlantic is cold, he says, “more snow on the Tibetan plateau in spring and early summer uses up all the sun’s heating, because it has to be melted and evaporated before the land can warm.”
• Should the ocean conveyor falter in the coming years, the effects for Asia could be even more grievous than for Europe. The tropical school disagree with this analysis.
PART VII. AT THE MILLENNIUM
Chapter 32: The Heat wave. The year Europe felt the heat of global warming
• This was by no standards an ordinary summer heat wave. For one thing, it killed at least 35,000 people: 20,000 in Italy and 15,000 in France. At the heat wave’s peak, on August 13, 2003, the 24-hour death toll in Paris was 8 times the norm.
• This was the first single weather event that climate scientists felt prepared to say was directly attributable to man-made climate change.
• The French mathematician Pascal Yiou, of the Laboratoire des Sciences du Climat et de l’Environnement, collected 600 years’ worth of parish records showing when the Pinot Noir grape harvest began in the Burgundy vineyards of eastern France.
• There was a clear relationship between summer temperatures and the start of the harvest, so he extrapolated backward to produce a temperature graph from the present to 1370. The results showed that temperatures as high as those typical in the 1990s were unusual, but had happened several times before.
• “However,” Yiou said, “the summer of 2003 appears to have been extraordinary, unique.” Temperatures in Burgundy that year were almost 11°F above the long-term average.
• The highest previous temperature had been just 7° above the average. That happened in 1523, in a warm interlude during the little ice age.
• Allen says that by mid-century, if current warming trends persist, the extreme temperatures experienced in Europe could occur on average once every 2 years.
• For people living in cities, the risks are greater because of the “urban heat island effect.” The air just stays in the streets and cooks.
Chapter 33: The Hockey Stick. Why now really is different
• If you lay a hockey stick on the ground and look at its shape as a graph, you will see that the long, flat shaft has at the end of it a short but sharply upturned blade. That, according to the IPCC authors published in 2001, is the shape of the world’s temperatures over the past thousand years: about 900 years of little or no change, followed by a century with a short, sharp upturn.
• Mike Mann was accused of concocting a spurious case that late-20th-century warming was exceptional and therefore, presumably, a result of man-made pollution. Soon Mann was fraud-of-the-month on the Web sites of climate sceptics.
• I will now entertain some of the criticisms that have rained on Mann, because they matter. But it is worth saying first that nothing I have heard impugns Mann’s scientific integrity, credentials, or motives. He is just braver than some, and more willing to have his debates in public – and to fight back when the brickbats start flying. (You can read him in action on www.realclimate.org.)
• Some researchers have suffered real personal and psychological damage from attacks by sceptics. I hope that won’t happen to Mann. I wish more scientists were like him.
• The subtext of the climate sceptics assault on Mann’s hockey stick has always been that if the current warming is shown not to be unique, then somehow the case that man-made global warming is happening evaporates.
• Keith Briffa, a respected British tree-ring analyst at the University of East Anglia, is not alone in arguing precisely the opposite. If it was indeed very warm globally in the medieval warm period, that is truly worrying, he says. “Greater long-term (natural) climatic variability implies a greater sensitivity of climate to forcing, whether from the sun or greenhouse gases. So greater past climate variations imply greater future climate change.”
Chapter 34: Hurricane Season. Raising the storm cones after Katrina
• The year 2005 was an extraordinary one in the Atlantic. There were so many tropical storms that for the first time meteorologists ran out of names for them. It was the second hurricane year in a row to be described by meteorologists as “exceptional” and “unprecedented,” and it came after a decade of rising hurricane activity that stretched the bounds of what had previously been regarded as natural.
• Hurricanes had been strong before, from the 1940s through the 1960s. There have always been hurricanes. Worldwide there are about 85 tropical cyclones each year, of which about 60 reach hurricane force. But the distribution of the hurricanes varies a great deal from year to year. In 2005 the Atlantic was battered but the Pacific was relatively peaceful.
• On the face of it, global warming is likely to make things worse. The initial pillar of humid air forms only when the temperature of the sea surface exceeds 78°F. As the world’s oceans warm, ever-larger areas of ocean exceed the threshold. There has been an average ocean warming in the tropics of 0.5 degrees already.
• When Katrina went from a category 1 to a category 5 hurricane, the surface of the Gulf of Mexico was around 86°F, which, so far as anyone knows, was a record.
• This simple link between sea surface temperatures and hurricane formation and strength has encouraged the view that a warmer world will inevitably lead to more hurricanes, stronger hurricanes, and the formation of hurricanes in places formerly outside their range.
• The veteran forecaster William Gray of Colorado State University says that what actually drives the updrafts that create the storm clouds is not the absolute temperature at the sea’s surface but the difference in temperature at the top of the storm. The hurricane-generating potential of the tropics may remain largely unchanged.
• Most tropical storms fizzle out because they lose contact with their fuel – the heat of warm ocean waters. This happens most obviously when a hurricane passes over land, but it also happens at sea.
• A hurricane can grow only if the warmth extends for tens of yards or more below the surface. But with every year that passes, warm water is penetrating ever deeper into the world’s oceans. That is clearly tied to global warming.
• Katrina continued to strengthen as it headed towards New Orleans, because it moved over water in the Gulf of Mexico that was very warm, not just at the surface but to a depth of more than 300 feet.
• The 1998 season was the first in a 100-year record when, on September 25, 4 hurricanes were on weather charts of the North Atlantic at one time. Not long afterward came Hurricane Mitch, the most destructive storm in the Western hemisphere for 200 years. The Atlantic is also generating hurricanes in places where they have never been seen before.
• The biggest source of hurricanes is, and is likely to remain, in the western Pacific, where they terrorize vulnerable and densely populated nations like the Philippines, Vietnam, and China.
• Kerry Emanuel has concluded that, on average, storms are lasting 60% longer and generating wind speeds 15% higher than they did back in the 1950s. Damage done by a hurricane is proportional not to the wind speed but to the wind speed cubed. Emanuel’s results suggest that the destructive power of a typical hurricane has increased by an alarming 70%.
• Only weeks after Emanuel’s paper appeared, in the autumn of 2005, three other leading hurricane researchers published a similar alarming conclusion. The frequency of the strongest storms – categories 4 and 5 – had almost doubled since the early 1970s.
• They now make up 35% of the total, compared with 20% just three decades before. The trend was global and clearly connected to the worldwide rise in sea surface temperatures. “We can say with confidence that the trends in sea surface temperatures and hurricane intensity are connected to climate change,” Curry declared.
• William Gray and some other traditional hurricane forecasters have contested the findings. But even if we don’t yet see “superhurricanes,” evidence is emerging of a human fingerprint in the rising number of stronger, longer-lasting hurricanes. It is not yet proof.
• There is no dispute that, taken together, hurricanes have been doing a lot more damage in recent years. That trend seems set to continue.
PART VIII. INEVITABLE SURPRISES
Chapter 36: The Dance. The poles or the tropics? Who leads in the climate dance?
• Researchers into the global history of climate divide into two camps. One believes that the key drivers for past, and therefore probably future, climate change lie in the polar regions, especially the far North Atlantic. The other believes that the real action happens in the tropics.
• After some years of standoff, many protagonists in this debate are now seeking common ground. Paul Crutzen has been in the forefront of research in both spheres, helping crack the mysteries of the Antarctic ozone layer while making a strong case for the dynamic properties of the tropical heat engine.
• “Big planetary changes happen in both the tropics and the very high latitudes,” he says. “The tropics are where the high temperatures drive a lot of the chemistry and dynamics of the atmosphere. And the polar regions are the homes of the big natural feedbacks that could accelerate climate change: things like melting ice and permafrost and alterations to ocean currents.” That is probably as good a compromise statement as can be found right now. At the end of the day, the system is bigger than the individual parts.
Chapter 37: New Horizons. Feedbacks from the stratosphere.
• Constantly, in writing this book, I have been struck by how little we know about the way Earth’s climate and its attendant systems, feedbacks, and oscillations function.
• This story contains some heroic guesses, some brilliant intuition, and, no doubt, occasionally some dreadful howlers – because that is where the science currently lies. More questions than answers.
• Richard Alley must be right that there are more “inevitable surprises” out there – outcomes that nobody has yet thought of, let alone tested. If anyone doubts that plenty of new surprises are waiting to be discovered, then the work by Drew Shindell, of the Goddard Institute for Space Studies (GISS), should offer food for thought.
Conclusion: Another Planet
Over the past 100,000 years, there have been only two generally stable periods of climate, according to Richard Alley. The first was “when the ice sheets were biggest and the world was coldest,” he says. “The second is the period we are living in now.” For most of the rest of the time, there has been “a crazily jumping climate.” And now, after many generations of experiencing global climatic stability, human society seems in imminent danger of returning to a world of crazy jumps. We really have no idea what it will be like, or how we will cope. There is still a chance that the jumps won’t materialize, and that instead the world will warm gradually, even benignly. But the odds are against it. There are numerous feedbacks – waking monsters, in Chris Rapley’s words – waiting to provide the crazy jumps. Climatically, we are entering terra incognita.
The current generation of inhabitants of this planet is in all probability the last generation that can rely on anything close to a stable global climate in which to conduct its affairs. Jim Hansen gives us just a decade to change our ways. Beyond that, he says, the last thing we can anticipate is what economists call “business as usual.” It will be anything but. “business as usual will produce basically another planet,” says Hansen. “How else can you describe climate change in which the Arctic becomes an open lake in summer, and most land areas experience average conditions not experienced before even in the most extreme years?”
I am sorry if you have got this far hoping for a definitive prognosis for our planet. Right now, the only such prognosis is uncertainty. The Earth system seems chaotic, with the potential to head off in many different directions. If there is order, we don’t yet know where it lies. No scenario has the ring of certainty. No part of the planet has yet been identified as holding an exclusive key to our future. No feedback is predestined to prevail. On past evidence, some areas may continue to matter more than others. But “the story of abrupt climate change will become more complicated before it is finished,” as Alley puts it. “We have to go looking for dangerous thresholds, wherever they may be.”
• For now we have checklists of concerns. Quite a lot of this book has been taken up with climatic history. It works not, generally, through gradual change but through periods of stability broken by sudden drunken lurches. The past operation of the climate system reveals in their fully conscious state the monsters we may be in danger of waking.
• In 1989, in a book called Turning Up the Heat, I warned that we passengers could no longer sit back for the ride. We needed to get hold of the controls or risk disaster.
• 15 years on, the urgency of the climate crisis is much clearer, even if the story has grown a little more complicated. But we are showing no signs yet of acting on the scale necessary. Even at this late hour, I do believe we have it in our power to set Spaceship Earth back on the right course.
• In the past, if we got things wrong and wrecked our environment, we could pack up and move somewhere else. Migration has always been one of our species’ great survival strategies.
• Now we have nowhere else to go. No new frontier. We have only one atmosphere; only one planet.