“Past performance does not necessarily predict future results”–
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Missing glaciers in the Canadian Selkirks. S. Mulkey.
Climate behaves in some ways like the financial system. As shown by the crashes of 1929 and 2008, the financial system is a complex system of interdependent parts which collectively can abruptly shift to a new state. Similarly, Earth systems can shift abruptly when external conditions drive them to alternative states. Tipping points in the Earth’s climate system and associated biosphere components have been defined by Tim Lenton and colleagues (2008) as large-scale components of the Earth’s systems that may pass a critical threshold and abruptly change function under anthropogenic forcing. Such shifts into a qualitatively different state of functioning can occur with little warning after extended periods of relatively little change. Treating our biosphere and climate as predictable based on their behavior over the most recent 10,000 years of the Holocene is like driving the car forward while looking in the rear view mirror (hat tip to climate scientist Katharine Hayhoe). Indeed, the Holocene geological epoch has been called the Goldilocks period because conditions were optimal for the development of agriculture and human civilization.
There has been a steady stream of research showing that the climate system has recently entered new and dangerous territory. I am uneasy using the experience of past decades of incremental change to guide our expectations of the impacts of clearly accelerating climate change. It is likely that we are in for surprises. Components of the Earth’s systems such as the Arctic are especially vulnerable to abrupt transition. I have been reticent to make such statements in the past, despite the evidence that our situation has been growing steadily worse, because the response variables measured by scientists are often not apparent to the public. I believe that within the next decade increases in climate-driven extreme events will be apparent to even the most disconnected city dweller.
The evidence that our situation is rapidly deteriorating comes from several different sectors of the climate system and biosphere.
- Studies of the rate of sea level rise validate what Miami dwellers know from direct experience. Since the beginning of this century there has been a dramatic increase in coastal tidal flooding along the Eastern U.S. coast, almost all of which is directly attributable to human caused warming of the oceans. Reports in the Proceedings of the U.S. National Academy indicate that the rate of sea level rise has quickened largely as a function of thermal expansion of surface waters.
- Superstorms and large cyclones have done immense damage over recent years. Although we cannot say that cyclonic storms are becoming more frequent, their size and power is consistent with warm oceans and generally greater energy aloft. Storm surge along the coasts of Europe and the U.S. has been significantly amplified by sea level rise, increasing property damage and loss of life.
- Several recent papers indicate that somewhere between 3 and 4 feet of sea level rise is a reasonable expectation by 2100 relative to 2000, assuming emissions are not drastically curtailed. Globally, more than 150 million people live within 3 feet elevation of the ocean. A recent analysis in Nature Climate Change shows that, accounting for population growth, 3 feet of sea level rise will displace about 4.2 million people in the U.S. by the end of the century. It should be obvious that there is no feasible infrastructure solution to sea level rise of this magnitude. For reasons related to the physics of the Earth rotation and the mass of the water involved, the increase will be especially pronounced on the Atlantic Coast of North America as the Gulf Stream slows in response to immense volumes of cold, freshwater dumping into the North Atlantic from the melting ice sheets of Greenland. The only responsible course at this point is to begin the process of strategic retreat from coastlines.
- Recently greenhouse gas concentrations have entered territory not seen in at least 3 million years. During the Pliocene the concentration of CO2 was equivalent to that of today at 400 ppm, a milestone officially surpassed in March 2015. Temperatures were 2-3˚C higher and sea level was 25 meters higher. Measurements at the NOAA facility at Mauna Loa, Hawaii, show that 2015 witnessed the highest rate of growth in CO2 levels ever recorded in a single year. This rate of rise was faster than in several hundred thousand years. Although equilibrium sea level in response to such warming will take several centuries, the transition to above 2˚C would be much faster and wreak havoc with much of the biosphere as we know it. It is important to realize that we still have some time to mitigate warming and adapt to the likely changes in the Earth’s systems if we act decisively and soon.
- The closing months of 2015 and the beginning of 2016 have broken all records for global warmth. February was the most abnormally warm month by a breathtaking margin. Experts such as Stefan Rahmstorf agree that the current strong El Niño has made a contribution to these extreme temperatures, but overall warming of the oceans and the lower atmosphere is accelerating. Moreover, recent work on aerosols shows that until recent years, warming has been masked by particulate pollution throughout much of the northern hemisphere. As skies have cleared, warming has been more fully expressed. Briefly in February the global mean temperature was 2˚C above the preindustrial average for the first time in history.
- This astonishing escalation in global temperature is occurring at the same time that Arctic sea ice has reached a new record low during the Arctic winter (graph below from the National Snow and Ice Data Center).
- The photosynthetic surface of the Earth usually takes up more greenhouse gas than it releases, but for the first time since studies have been conducted the terrestrial biosphere is now a net source of warming gases. Methane and nitrous oxide emissions from agriculture, apparently mostly from Asia, are the major new contributors to the greenhouse gas burden of the atmosphere. Some scientists have disputed this, noting that the steep rise in methane may be from the fracking boom, primarily in the U.S. Some progress has been made in reforestation, which all else remaining stable, should have resulted in more CO2 removed from the atmosphere. Overcoming this new positive feedback to warming of the climate system will require us to redouble our efforts at reducing emissions from fossil fuels.
- Massive peat fires in Indonesia and wildfires in the American West of historic magnitude are now a common occurrence, made more likely by climate driven factors such as drought, pests, and warming. It is likely that the frequency and magnitude of these fires will escalate in the coming years.
- Extreme drought across the Amazon basin may now be a regular occurrence, resulting in the death of old trees, a major source of uptake of CO2 in the rainforest, and impaired photosynthesis of remaining trees.
- As the permafrost region of earth continues to warm, its large pool of carbon has begun to increasingly decompose, burn, or be exported by hydrological processes. Presently photosynthesis during the progressively longer growing season is inadequate to offset increasing carbon loss. Recently 98 permafrost-region experts noted that this region will become a net carbon source to the atmosphere by 2100 regardless of the warming scenario. Net emissions from this source can be reduced, however, if warming is slowed. A tipping point has been passed for the tundra.
- The world’s corals are experiencing the third and most extreme bleaching event of this century. Although the previous two events have resulted in permanent damage, the current event is likely to have major, lasting impacts, damaging food chains and fisheries for decades to come. The progressive death of this fragile system is a clear indication that dangerous climate change has arrived.
- Perhaps the most stunning finding of 2015 is that the massive Western Antarctic Ice Sheet is now committed to eventual collapse owing to currents in the warming Southern Ocean. This appears to be unstoppable and over a period of a few hundred years will contribute more than 3 meters (~10 feet) to the increase in global sea level. The most important implication of this is not the eventual contribution to sea level rise, but that even in the apparently stable cold of Antarctica, climate change is having a profound impact that is now irreversible.
The U.S. National Academy has presented the first ever analysis of attribution of anthropogenic climate change to weather extremes of various forms. Dr. Jeff Masters at the Weather Underground has posted a thoughtful review of this work. Although some extreme phenomena have no relationship to global warming, many are either driven or affected to some degree by climate change. Masters notes that the way one poses the question of attribution is critically important. Indeed, it is reasonable to consider that all weather is now occurring in a human altered climate. Thus, it is more appropriate to assess which features of an event have been influenced by climate change, than to ask whether or not the event was caused by climate change.
In terms of the impact of increasing temperatures on living systems, it is the extremes that matter the most. According to the review, high temperature extremes can be attributed to climate change with considerable confidence. The figure below shows the relative contribution of human caused climate change to extreme high temperatures over much of the 20th century to the present. It is unlikely that most of these extreme events would have occurred in the absence of global warming.
Several researchers are now saying publically that staying below the putative guardrail of 2˚C global average warming relative to preindustrial temperatures is very unlikely or even impossible. At the Paris climate meetings in December 2015, 196 nations agreed to a plan for achieving 2˚C, and stated their intention to meet 1.5˚C if possible. This is striking given research published in Science in 2005 by Gerald Meehl and team which shows that with heat stored in the oceans, the Earth is committed to an additional .5˚C warming on top of the then ~0.8-0.9˚C warming since preindustrial times. This assumes that the concentrations of greenhouse gases of the atmosphere could be held stable, which is impossible. There is no enforceable means to ensure that either of the Paris goals will be met, but the fact that the agreement exists with pledges from so many nations represents a watershed for international cooperation. Climate correspondent for the Washington Post Chris Mooney notes that the “magic number” of 2˚C has little scientific basis and is not necessarily an indicator of a safe level of climate change. Moreover, simple math indicates that at current rates we will exceed our remaining emissions budget before 2030.
There are hopeful signs with respect to alternative energy production. In some parts of the world, wind and solar energy are at, or very close to, grid parity with fossil fuel sources of energy in terms of cost per kilowatt hour. The rate of installation of renewable energy infrastructure has vastly exceeded expectations of just 5 years ago. With the rise of natural gas and renewables, the most polluting source of energy, coal, has collapsed in market value. The majority of plans for new coal fired power plants in North America have been abandoned and several existing plants are being closed. Partly because of the rise of alternative renewable energy sources, the International Energy Agency in Paris reports that global emissions from energy production have remained flat while the global economy has grown during 2014 and 2015. Unfortunately, in several U.S. states the scions of the fossil fuel industry are fighting a rearguard action, persuading or bribing lawmakers and utilities to impose taxes and fees on renewables in an effort retain market share. It seems unlikely that these regressive forces can prevail for very long, but it remains to be seen if we can install clean forms of energy in sufficient capacity to avoid catastrophic warming of 4-5˚C this century.
Taken together, these data are as sobering as any I have seen in my 35 year career. Are we about to drive the car off the cliff while looking in the rear view mirror? Maybe. I am alarmed that our political leaders and planners continue to look at the future as if it will be mostly like the 20th century. The science is clear that nothing could be farther from the truth. No one can say for sure when the impact of these ongoing changes will become so severe that the threads that hold civilization together will begin to stretch beyond the breaking point. Given recent events, I can say with confidence that such a day will come sooner rather than later if we do not step up our game. Through implementation of strong mitigation of emissions and proactive adaptation to emerging changes in Earth systems, there is still time to build a bright future for our kids. What continues to astonish me is that we seem to be willing to keep poking the beast long after it has risen on its haunches and bared its fangs, all the while debating whether or not the beast is dangerous.