Tipping Points

Definition

Twelve tipping points that could lead to drastic and irreversible changes in our global environment.

Source: PIF. Author: PIF. Permission: Fair Use / Permission pending.

Malcolm Gladwell's book, The Tipping Point: How Little Things Can Make a Big Difference¹ popularized use of the term 'tipping point.'  Gladwell takes the traditional use of tipping point, the name given to that moment in an epidemic when a virus reaches critical mass, and examines how tipping points can also occur when ideas, behaviors and new products move through a population. One thrust of Gladwell's book is that when tipping points are passed, momentum for change can become unstoppable.

In 2008, a team of scientists published the first detailed examination of possible tipping points in the Earth's climate system brought about by human-induced activities.  In an article, Tipping elements in the Earth's climate system, the authors, Timothy Lenton of the University of East Anglia and his collaborators, describe a "tipping point" as the "critical threshold at which a tiny perturbation can qualitatively alter the state of development of a system."²   They also introduce the term "tipping element" to describe those Earth's subsystems, at least subcontinental in scale, which can be switched into a "qualitatively different state by small perturbations."³  

In the article, the authors examine policy relevant potential future tipping elements in Earth's climate system, temperature increases which could trigger those tipping points, and possible time frame for when those tipping points could be crossed. They examine fifteen of the Earth's subsystems: Arctic sea ice, the Greenland ice sheet, the West Antarctic ice sheet, the Atlantic thermonhaline circulation, the El Niño-southern oscillation, the Indian monsoon, the Sahara/Sahel and West African monsoon, the Amazon Rainforest, the Boreal Forest, Antarctic Bottom Water, Tundra, Permafrost, Marine methane hydrates, Ocean anoxia, and the Arctic ozone. By synthesizing present knowledge of climate change, they conclude that a variety of tipping points could be reach within this century, with the greatest immediate threat to Arctic sea ice.⁴

The term tipping point is now widely used by those wishing to describe a situation where global warming leads to rapid and abrupt, often called "non-linear," climate change with potentially dangerous or catastrophic consequences, and to underscore that society should not be lulled into a sense that changes to our earth's climate systems will be gradual,  or "linear," thereby giving humankind the time to address greenhouse gas emissions and prepare for any changes to the climate.⁵ However, 'dangerous' climate change can occur before tipping thresholds are reached, so the terms should not be synonymous with one another. 'Irreversible' climate change, on the other hand, is closely linked with tipping points. Once a system tips, it tends to remain at a new state of equilibrium, making it very difficult to return to the previous state.

Historical perspective

Earth's climate has experienced wide climatic variability throughout its history. The changes often occur gradually over time, influenced by a number of factors on various time-scales. Some shifts in climate, however, have occurred at an accelerated rate, often initiated by a relatively small change in the climate system, leading to a dramatic, sustained change in the climate. The planet's historical record provides evidence of many of these non-linear changes, or tipping points, in the climate. Unlike current human-induced climate change, these events have been part of the Earth's natural climate variation.

Fifty-five million years ago, equatorial temperatures rose by 4-5 °C within a few thousands years. Temperature increases at the poles were twice as large. This temperature spike in a relatively short time is referred to as the Paleocene-Eocene Thermal Maximum (PETM), and the climate system took hundreds of thousands of years to recover. The event was caused by the release of 1500-4500 gigatons of carbon into the atmosphere, which greatly enhanced the concentration of greenhouse gases.⁶ The source of the carbon is uncertain, but may have come from a large burn-off of fossil fuels in the emerging North Atlantic due to volcanic intrusions, and/or the destabilization of underwater methane hydrates. Likely, a small increase in temperature initiated a wide-spread breakdown of the methane hydrates, causing large quantities of methane to enter the atmosphere.  The increases in atmospheric methane, a potent green house gas, would have greatly increased the initial rate of global warming.  In this scenario, the collapse of methane hydrates would be considered to be a tipping point in the climate system.⁷

Past instances of dramatic decreases in Earth's temperature provide additional cases where possible tipping points may be identified.  Ice ages, for example, typically begin in a non-linear fashion. As the Earth starts to cool, ice coverage at the poles increases. Because of its highly reflective nature, most of the solar energy that hits ice sheets is deflected back into space rather than absorbed. This is referred to as the albedo effect. Polar ice coverage and the resulting solar reflectivity eventually reach a tipping point. Expanding ice coverage creates a positive feedback system that further drives down temperature, as more ice means less heat absorbed by the Earth. This, in turn, promotes further ice growth and ice stability that lead to prolonged ice ages. An extreme example of this is the so-called "snowball Earth" over 700 million years ago, when most of the planet was covered by snow and ice. Such substantial ice coverage was achieved by a tipping of the system away from absorbing incoming solar energy.⁸

Current research

One active area of research is the attempt to more accurately model the interactions of the varying tipping processes. For example, there are models that project how warming temperatures will affect both the permafrost thaw and ice melt, and how each will drive greater temperature increases, but there is little analysis in the ways these elements will all drive one another (and other variables) to further accelerate climate change.

Another area of research looks at what temperature and/or atmospheric concentration of GHGs might be the tipping point of various systems. The desire to avoid tipping points has been at the center of the debate over a safe upper limit for CO2 atmospheric concentrations. The average concentration of carbon dioxide (CO2) in 2009 was 387 parts per million (ppm), with an annual increase of 2 ppm.⁹ A target of 450 ppm has been advocated to avoid 'dangerous' climate change, and under business as usual the world will reach that target before 2040. Dr. James Hansen, Director of NASA Goddard Institute for Space Studies, has countered that 450 ppm in not sufficient to avoid consequential climate tipping points, and concluded that 350 ppm, roughly the concentration in 1990, is the safe upper limit.¹⁰ While this debate will continue, it is highly likely that CO2 concentrations will climb much higher than either number.

Despite the focus on CO2, other GHGs are having a significant impact on short-term temperature increases. Methane is the most significant of these other gases. As opposed to CO2, which lasts in the atmosphere for more than a century, methane lasts for approximately 12 years. In its lifetime, one kilogram of methane is 56 times more potent in trapping heat than one kilogram CO2 is over 20 years. As a result, global methane emissions in 2005, over the course of their lifetimes, will cause temperature increases equivalent to the effect that 62% of 2005 CO2 emissions will have over the next 20 years. Black carbon, or soot, is another powerful global warming agent, despite a lifetime of only a week. Despite its short life, one kilogram of black carbon is 1,600 times more powerful during its life than one kilogram of CO2 is over 20 years. A conservative estimate is that 2005 black carbon emissions produced as much warming as 47% of what 2005 CO2 emissions will cause over 20 years. The potency of CO2 is bigger if one considers its contributions to temperature increases over its lifetime. However, the risk of near-term tipping points requires policy makers to consider the short-term warming implications of different gases.¹¹

Current research indicates that the increase in GHGs since the start of the industrial era has locked in a global temperature increase of 2.4°C (1.4-4.3°C). Of this, 0.6°C having already occurred, meaning the world is committed to an increase of an additional ~1.5°C, most of which will occur this century. Emissions mitigation efforts will only slow additional temperature increases over this 1.5°C rise.¹² This puts the world on track to reach many of the tipping point temperatures for various systems, indicated in Table 1 below, during this century. Two of the most sensitive systems are the Greenland ice sheet and the Arctic sea ice, whose tipping points lie within a 2°C increase.¹³

Systems that could tip

To examine possible tipping points in the earth's systems, the authors of the article, Tipping elements in the Earth's climate system, gathered data, reviewed literature and solicited opinions from climate experts on potential tipping elements in the earth's climate systems. Table 1 (right) outlines nine of the most policy-relevant tipping elements they examined, the amount of global warming needed to cause the elements to tip, the timescales for warming, and a summary of key impacts of the warming.  They conclude that the Greenland ice sheet and Arctic summer ice exhibit the highest sensitivity and the smallest uncertainty, and that the tipping elements in the tropics, the boreal zone, and West Antarctic have a significant amount of uncertainty surrounding them, but that "given their potential sensitivity, constitute candidates for surprising society." ¹⁵

The authors of this study conclude that summer Arctic sea ice may be lost within 10 years.  A number of other climate scientists note that albedo feedback makes summer and fall sea ice sensitive to moderate increases in temperature and that studies have shown that once sea ice retreats to a certain point, remaining ice can be lost without additional temperature increases.¹⁶   Concerns that the Arctic may have crossed a tipping point have been rekindled by recent observations establishing that the Arctic has been melting much more quickly than many scientists had predicted.¹⁷

Significant changes in the Arctic environment could lead to dramatic swings in weather and climate patterns across the rest of the globe, with potentially far-reaching consequences for ecosystems and human populations.  The influx of large amounts of freshwater into the northern Atlantic Ocean from a melting Arctic ice cap, for example, and the Greenland ice sheet, may alter the Atlantic Themohaline Circulation, which brings warm water north from the Caribbean to North Europe.  According to some scientists, a change is this circulation that might occur in next 100 years if current climate trends are not reversed.¹⁸   The collapse of one system may lead to the collapse of other systems, causing highly disruptive changes over relatively short time periods.¹⁹ Dr. James Hansen has warned that the earth's climate system is reaching dangerous tipping points, that "elements of a 'perfect storm', a global cataclysm, are assembled."  Hansen warns that, "The tipping point for life on the plant will occur when so many interdependent species are lost that ecosystems collapse."²⁰

Criticism

Criticism of tipping points has largely two main thrusts.  The first questions the scientific certainty of future tipping points. Some have challenged the assertion that non-linear changes in the climate will likely occur in the near future. These critics maintain that high degrees of uncertainty exist over tipping points, including at what point they would occur or how much they would affect the rate of climate change. These experts worry that tipping point predictions that prove untrue will hamper the efforts to reduce emissions by reducing the public's trust in scientists' predictions and their calls for robust and rapid action to address climate change.²¹

The second main criticism of tipping points focuses on its policy implications. Some, including some members of the scientific community, have expressed concerns that discussion of tipping points will hurt the effort to mitigate climate change. They fear that if it is determined that a tipping point has been passed, the public will conclude that the window of opportunity has passed to slow the effects of climate change. This will in turn, they say, halt the momentum to reduce carbon emissions and give politicians an excuse for inaction. They do not dispute the existence of climate tipping points, but believe it most useful for governments and the public to view climate change on a continuum and that no emission reduction is too late or less valuable. They are concerned that a focus on tipping points result in populations no longer feeling empowered or obligated to reduce their carbon emissions.²²

Fast track mitigation strategies

Scenario of Global Emissions Reduction Pathways to Avoid ›2°C

Source: EDF. Author: Wagner et al. 2009. Permission: Fair Use.

The existence of possible tipping points in Earth's systems in the near future from human activities gives added impetus for the global community to develop fast track strategies to address climate change.  Most scientists agree that at the heart of any strategy must be a path to decrease CO2 and other greenhouse gas emissions as rapidly as possible and to address other non-CO2 elements that affect climate change.  CO2 is the main driver of global warming , and is particularly dangerous to the climate because it will stay in the atmosphere for over a century after emissions stop.²³ . Such efforts must involve long terms strategies to improve energy efficiency and the increase use of non carbon-based energies.²⁴  

Other strategies exist to reduce non-CO2 elements and could complement efforts to reduce and eliminate CO2 emissions.  These include:

• Reducing black carbon in the atmosphere - Black carbon, or soot, is a major contributor to global warming. It absorbs heat in the atmosphere and reduces albedo when deposited on snow and ice.  It results from biomass burning, cooking with solid fuels and diesel exhaust.  Problems arising from soot in the atmosphere are particularly acute in the developing world. Several reports have suggested that because black carbon remains in the atmosphere for only a few weeks, reducing black carbon emissions could provide immediate climate change benefits at a relatively low cost, while providing important co-benefits, such as improving air quality and public health.²⁵

• Accelerating the phase out of Ozone Depleting Substances (ODS) - Many ozone depleting substances covered under the Montreal Protocol are powerful greenhouse gases.  The phase out of certain ODS in support of the Montreal Protocol has resulted in green house gas reductions equivalent to several billion tons of CO2. In September 2007, the Parties agreed to an accelerated phase out of HCFCs and took steps to prevent emissions of ODS for existing stockpiles.  Ensuring the rapid phase out of ODS with global warming potential and the destruction of existing stockpiles will also provide important and relatively quick climate change benefits.²⁶

• Increase bio-sequestration of forests and soils - Bio-sequestration refers to the process by which CO2 is removed from the atmosphere and stored in vegetation, soils and sediments. Increasing bio-sequestration of forests and soils is one way to mitigate the accumulation of CO2 in the atmosphere.  Afforestation and reforestation, for example, can sequester CO2 over decades, even centuries, until the systems reach the stage of carbon saturation. The use of biochar in soils, a carbon-rich product obtained from the pyrolysis of biomass, is another example of bio-sequestration.²⁷

Footnotes

1. Gladwell, Malcolm, The Tipping Point: How Little Things Can Make a Big Difference, Little Brown, 2000

2. Timothy Lenton, Herman Held, Elmar Kreigler, Jim W. Hall, Wolfgang Lucht, Stefan Rahmstorf and Hans Joachim Schellnhuber, Tipping elements in the Earth's climate system, Proc of the Nat'l Acad Sci USA 1786 -1793 (2008).

3. Lenton et al. Tipping elements in the Earth's climate system at 1786. 2008.

4. Lenton et al. Tipping elements in the Earth's climate system at 1788-1791. 2008.

5.  See for example, T.W. Lenton.  Tipping points in the Earth system.   Personal web page.  Updated June 3, 2009.

6. T.W. Lenton. Tipping points in the Earth system. Personal web page. Updated June 3, 2009.

7. T.W. Lenton. Tipping points in the Earth system. Personal web page. Updated June 3, 2009.

8. T.W. Lenton. Tipping points in the Earth system. Personal web page. Updated June 3, 2009.

9. NOAA. Trends in Atmospheric Carbon Dioxide - Mauna Loa. June 2009.

10. A. Revkin. Back to 1988 on CO2, Says NASA’s Hansen. NY Times: Dot Earth. 19 March 2008.

11. CO2 and methane emissions data from the WRI Climate Analysis Indicators Tool.  Black carbon emissions data from the Center of  Global and Regional Environmental Research ARCTAS inventory.  Equivalence calculations were guided by the ICCT's A policy-relevant summary of black carbon climate science and appropriate emission control strategies, from June 2009.

need to cite this paragraph, will complex: include CAIT, Ramathan, UNFCCC, and others

12. V. Ramanathan and Y. Feng, On avoiding dangerous anthropogenic interference with the climate system: Formidable challenges ahead, Proceedings of the National Academy of Sciences 105 (38), 14245-14250, Sep 23, 2008.

13. Lenton et al. Tipping elements in the Earth's climate system at 1786. 2008.

14. Based on Table 1, Policy-relevant potential future tipping elements in the climate system, in Tipping elements in the earth's climate system,  at 1788

15. Lenton et al. Tipping elements in the Earth's climate system at 1788-1791.

16. Lenton et al. Tipping elements in the Earth's climate system at 1788.

17. Steve Cole, Alan Buis, New NASA Satellite Survey Reveals Dramatic Sea Ice Thinning, Goddard Space Flight Center, July 7, 2009.

18. Lenton et al. Tipping elements in the Earth's climate system at 1788-1790.

19. Mike Bettwy, Changes in the Arctic: Consequences for the World, Goddard Space Flight Center, updated February 23, 2008

20. James Hansen, Twenty Years Later: Tipping Points Near on Global Warming, The Huffington Post, June 25, 2008.

21. A. Revkin. Among Climate Scientists, a Dispute Over 'Tipping Points'. New York Times. Mar 29, 2009.

22. A. Revkin. Among Climate Scientists, a Dispute Over 'Tipping Points'. New York Times. Mar 29, 2009.

23. IPCC, 2007: Summary for Policy Makers. In: Climate Change 2007: The Physical Basis: Contribution of Working Group 1 to the Fourth Assessment Report to the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)], Cambridge University Press, Cambridge, United Kingdom, and New York, NY, USA.

24. IPCC, 2007, Summary for Policymakers. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY USA.

25. V. Ramanathan and G. Carmichael. Global and regional climate changes due to black carbon. Nature Geoscience 1, 221 - 227 (2008).

26. US Environmental Protection Agency. Ozone Science: The Facts Behind the Phaseout. August 2008.

27. U.S. Department of Energy, Carbon Cycling and Biosequestration: Integrating Biology and Climate through Systems Science, December 2008. 

Resources

News Sources

J. Hansen, Coal-fired power stations are death factories. Close them. The Observer. February 15, 2009.

NASA-GISS.  Research Finds That Earth's Climate is Approaching 'Dangerous' Point.  Press Release. May 30, 2007.  (note: corresponds to Hansen et al. 2007)

Potsdam Institute for Climate Impact Research.  Tipping elements in the Earth's climate system.  Press Release.  Feb 4, 2008. (note: corresponds to Lenton et al. 2008)

A. Revkin.  Among Climate Scientists, a Dispute Over 'Tipping Points'.  New York Times.  Mar 29, 2009.

Reports

S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.).  IPCC: The Physical Science Basis. Working Group I to the Fourth Assessment Report  Cambridge University Press, 996 pp. 2007.

(Note: the IPCC doesn't have a "tipping point" section (or use the term almost at all), but rather discusses the various 'tipping point' phenomena throughout WG 1.  Chapters 3, 4, 5, and 10 are the best places to look)

UNEP.  Year Book 2009. (note: Ch 3 on climate change is the most useful)

Peter Schwartz & Doug Randall, An Abrupt Climate Change Scenario and it's Implications for United States National Security, (2003).

Journals

D. Archer, B. Buffett, and V. Brovkin.  Ocean methane hydrates as a slow tipping point in the global carbon cycle  Proceedings of the National Academy of Sciences: Nov 18, 2008.

J. Hansen et al. Dangerous human made interference with climate: a GISS model study  Atmospheric Chemistry and Physics 7: 2287-2312, 2007

E. Kriegler et al. Imprecise probability assessment of tipping points in the climate system Proceedings of the National Academy of Sciences 106 (13): 5041-5046, Mar 31, 2009.

R.W. Lindsay and J. Zhang. The Thinning of Arctic Sea Ice, 1988–2003: Have We Passed a Tipping Point? Journal of Climate 18: 4879-4894, 2005.

T.W. Lenton et al. Tipping elements in the Earth's climate system Proceedings of the National Academy of Sciences 105 (6): 1786-1793, Feb 12, 2008.

D. V. Khvorostyanov, P. Ciais, G. Krinner, and S. A. Zimov.  Vulnerability of east Siberia’s frozen carbon stores to future warming.  Geophysical Research Letters 35: L10703, May 20 2008.  (note: not available on line for free.  I accessed it through my college library and I'll send it to you.)

V. Ramanathan &Y. Feng, On avoiding dangerous anthropogenic interference with the climate system: Formidable challenges ahead, Proceedings of the National Academy of Sciences 105 (38), 14245-14250, Sep 23, 2008.

 J. Stroeve et al.  Arctic sea ice decline: Faster than forecast.  Geophysical Research Letters 34: L09501, 2007.

Miscellaneous

T.W. Lenton.  Tipping points in the Earth system.   Personal web page.  Updated March 6, 2009.