1 Lenton, T. M. et al. Tipping elements in the Earth's climate system. Proc. Natl Acad. Sci. USA 105, 1786–1793 (2008).

2 Smith, J. B. et al. Assessing dangerous climate change through an update of the Intergovernmental Panel on Climate Change (IPCC) 'reasons for concern'. Proc. Natl Acad. Sci. USA 106, 4133–4137 (2009).

3 Kriegler, E., Hall, J. W., Held, H., Dawson, R. & Schellnhuber, H. J. Imprecise probability assessment of tipping points in the climate system. Proc. Natl Acad. Sci. USA 106, 5041–5046 (2009).

4 Travis, W. R. Going to extremes: propositions on the social response to severe climate change. Climatic Change 98, 1–19 (2010).

5 Scheffer, M. et al. Early warning signals for critical transitions. Nature 461, 53–59 (2009).

6 Wissel, C. A universal law of the characteristic return time near thresholds. Oecologia 65, 101–107 (1984).

7 Kleinen, T., Held, H. & Petschel-Held, G. The potential role of spectral properties in detecting thresholds in the Earth system: application to the thermohaline circulation. Ocean Dynam. 53, 53–63 (2003).

8 Held, H. & Kleinen, T. Detection of climate system bifurcations by degenerate fingerprinting. Geophys. Res. Lett. 31, L23207 (2004).

9 Livina, V. N. & Lenton, T. M. A modified method for detecting incipient bifurcations in a dynamical system. Geophys. Res. Lett. 34, L03712 (2007).

10 Dakos, V. et al. Slowing down as an early warning signal for abrupt climate change. Proc. Natl Acad. Sci. USA 105, 14308–14312 (2008).

11 Lenton, T. M. et al. Using GENIE to study a tipping point in the climate system. Phil. Trans. R. Soc. A 367, 871–884 (2009).

12 Lenton, T. M., Livina, V. N., Dakos, V., van Nes, E. H. & Scheffer, M. Early warning of climate tipping points from critical slowing down: comparing methods to improve robustness. Phil. Trans. R. Soc. A (in the press).

13 Ditlevsen, P. D. & Johnsen, S. J. Tipping points: Early warning and wishful thinking. Geophys. Res. Lett. 37, L19703 (2010).

14 Hastings, A. & Wysham, D. B. Regime shifts in ecological systems can occur with no warning. Ecol. Lett. 13, 464–472 (2010).

15 Willoughby, H. E., Rappaport, E. N. & Marks, F. D. Hurricane forecasting: the state of the art. Nat. Hazard. Rev. 8, 45–49 (2007).

16 Titov, V. V. et al. Real-time tsunami forecasting: challenges and solutions. Nat. Hazard. 35, 35–41 (2005).

17 Sorensen, J. H. Hazard warning systems: Review of 20 years of progress. Nat. Hazard. Rev. 1, 119–125 (2000).

18 Verdin, J., Funk, C., Senay, G. & Choularton, R. Climate science and famine early warning. Phil. Trans. R. Soc. B 360, 2155–2168 (2005).

19 Thomson, M. C. et al. Malaria early warnings based on seasonal climate forecasts from multi-model ensembles. Nature 439, 576–579 (2006).

20 Basher, R. Global early warning systems for natural hazards: systematic and people-centred. Phil. Trans. R. Soc. A 364, 2167–2182 (2006).

21 United Nations Global Survey of Early Warning Systems: An Assessment of Capacities, Gaps and Opportunities Towards Building a Comprehensive Global Early Warning System for all Natural Hazards (United Nations, 2006).

22 Adams, R. M. et al. The benefits to Mexican agriculture of an El Niño-Southern Oscillation (ENSO) early warning system. Agr. Forest Meteorol. 115, 183–194 (2003).

23 Kim, M-K. & McCarl, B. The agricultural value of information on the North Atlantic Oscillation: yield and economic effects. Climatic Change 71, 117–139 (2005).

24 Solow, A. R. et al. The value of improved ENSO prediction to US agriculture. Climatic Change 39, 47–60 (1998).

25 Guilyardi, E. El Niño — mean state — seasonal cycle interactions in a multi-model ensemble. Clim. Dynam. 26, 329–348 (2006).

26 Chen, C-C., McCarl, B. & Adams, R. Economic implications of potential ENSO frequency and strength shifts. Climatic Change 49, 147–159 (2001).

27 Lenton, T. M. & Schellnhuber, H. J. Tipping the scales. Nature Rep. Clim. Change 1, 97–98 (2007).

28 Hansen, J. et al. Dangerous human-made interference with climate: a GISS model study. Atmos. Chem. Phys. 7, 2287–2312 (2007).

29 IPCC Climate Change 2007: Impacts, Adaptation and Vulnerability (eds Parry, M. L., Canziani, O. F., Palutikof, J. P., van der Linden, P. J. & Hanson, C. E.) (Cambridge Univ. Press, 2007).

30 Ramanathan, V. & Feng, Y. On avoiding dangerous anthropogenic interference with the climate system: Formidable challenges ahead. Proc. Natl Acad. Sci. USA 105, 14245–14250 (2008).

31 Zickfeld, K. et al. Expert judgements on the response of the Atlantic meridional overturning circulation to climate change. Climatic Change 82, 235–265 (2007).

32 Zickfeld, K., Morgan, M. G., Frame, D. J. & Keith, D. W. Expert judgments about transient climate response to alternative future trajectories of radiative forcing. Proc. Natl Acad. Sci. USA 107, 12451–12456 (2010).

33 Hansen, J. E. A slippery slope: How much global warming constitutes 'dangerous anthropogenic interference'? Climatic Change 68, 269–279 (2005).

34 Cook, K. H. & Vizy, E. K. Coupled model simulations of the West African monsoon system: twentieth- and twenty-first-century simulations. J. Clim. 19, 3681–3703 (2006).

35 Drijfhout, S., Weber, S. & van der Swaluw, E. The stability of the MOC as diagnosed from model projections for pre-industrial, present and future climates. Clim. Dynam. 10.1007/s00382-010-0930-z (2010).

36 Hargreaves, J. C. & Annan, J. D. Using ensemble prediction methods to examine regional climate variations under global warming scenarios. Ocean Model. 11, 174–192 (2006).

37 Hasselmann, K. Stochastic climate models part I. Theory. Tellus 28, 473–485 (1976).

38 Thompson, J. M. T. & Sieber, J. Predicting climate tipping as a noisy bifurcation: a review. Int. J. Bifurcat. Chaos 21, 399–423 (2011).

39 van Nes, E. H. & Scheffer, M. Slow recovery from perturbations as a generic indicator of a nearby catastrophic shift. Am. Nat. 169, 738–747 (2007).

40 Chisholm, R. A. & Filotas, E. Critical slowing down as an indicator of transitions in two-species models. J. Theor. Biol. 257, 142–149 (2009).

41 Wiesenfeld, K. & McNamara, B. Small-signal amplification in bifurcating dynamical systems. Phys. Rev. A 33, 629–642 (1986).

42 Surovyatkina, E. Prebifurcation noise amplification and noise-dependent hysteresis as indicators of bifurcations in nonlinear geophysical systems. Nonlin. Process. Geophys. 12, 25–29 (2005).

43 Carpenter, S. R. & Brock, W. A. Rising variance: a leading indicator of ecological transition. Ecol. Lett. 9, 311–318 (2006).

44 Biggs, R., Carpenter, S. R. & Brock, W. A. Turning back from the brink: Detecting an impending regime shift in time to avert it. Proc. Natl Acad. Sci. USA 106, 826–831 (2009).

45 Takimoto, G. Early warning signals of demographic regime shifts in invading populations. Popul. Ecol. 51, 419–426 (2009).

46 Guttal, V. & Jayaprakash, C. Changing skewness: an early warning signal of regime shifts in ecosystems. Ecol. Lett. 11, 450–460 (2008).

47 Dakos, V., van Nes, E., Donangelo, R., Fort, H. & Scheffer, M. Spatial correlation as leading indicator of catastrophic shifts. Theor. Ecol. 3, 163–174 (2010).

48 Guttal, V. & Jayaprakash, C. Spatial variance and spatial skewness: leading indicators of regime shifts in spatial ecological systems. Theor. Ecol. 2, 3–12 (2009).

49 Litzow, M. A., Urban, J. D. & Laurel, B. J. Increased spatial variance accompanies reorganization of two continental shelf ecosystems. Ecol. Appl. 18, 1331–1337 (2008).

50 Rietkerk, M., Dekker, S. C., de Ruiter, P. C. & van de Koppel, J. Self-organized patchiness and catastrophic shifts in ecosystems. Science 305, 1926–1929 (2004).

51 Bailey, R. M. Spatial and temporal signatures of fragility and threshold proximity in modelled semi-arid vegetation. Proc. R. Soc. B 278, 1064–1071 (2011).

52 Drake, J. M. & Griffen, B. D. Early warning signals of extinction in deteriorating environments. Nature 467, 456–459 (2010).

53 Thompson, J. M. T. & Sieber, J. Climate tipping as a noisy bifurcation: a predictive technique. IMA J. Appl. Math. 76, 27–46 (2011).

54 Kwasniok, F. & Lohmann, G. Deriving dynamical models from paleoclimatic records: Application to glacial millennial-scale climate variability. Phys. Rev. E 80, 066104 (2009).

55 Livina, V. N., Kwasniok, F. & Lenton, T. M. Potential analysis reveals changing number of climate states during the last 60 kyr. Clim. Past 6, 77–82 (2010).

56 Livina, V. N. et al. Changing climate states and stability: from Pliocene to present. Clim. Dynam. 10.1007/s00382-010-0980-2 (2011).

57 Bakke, J. et al. Rapid oceanic and atmospheric changes during the Younger Dryas cold period. Nature Geosci. 2, 202–205 (2009).

58 Levermann, A. & Born, A. Bistability of the Atlantic subpolar gyre in a coarse-resolution climate model. Geophys. Res. Lett. 34, L24605 (2007).

59 Wieczorek, S., Ashwin, P., Luke, C. M. & Cox, P. M. Excitability in ramped systems: the compost-bomb instability. Proc. R. Soc. A 467, 1243–1269 (2011).

60 Mann, H. B. Nonparametric tests against trend. Econometrica 13, 245–259 (1945).

61 Cunningham, S. A. et al. Temporal variability of the Atlantic meridional overturning circulation at 26.5° N. Science 317, 935–938 (2007).

62 Dow, K. & Cutter, S. L. Crying wolf: Repeat responses to hurricane evacuation orders. Coast. Manage. 26, 237–252 (1998).

63 Simmons, K. M. & Sutter, D. False alarms, tornado warnings, and tornado casualties. Weather Clim. Soc. 1, 38–53 (2009).

64 Jones, C., Lowe, J., Liddicoat, S. & Betts, R. Committed ecosystem change due to climate change. Nature Geosci. 2, 484–487 (2009).

65 Keller, K., Yohe, G. & Schlesinger, M. Managing the risks of climate thresholds: uncertainties and information needs. Climatic Change 91, 5–10 (2008).

66 Lenton, T. M., Footitt, A. & Dlugolecki, A. Major Tipping Points in the Earth's Climate System and Consequences for the Insurance Sector (WWF/Allianz, 2009).

67 Higgins, P. & Vellinga, M. Ecosystem responses to abrupt climate change: teleconnections, scale and the hydrological cycle. Climatic Change 64, 127–142 (2004).

68 Arnell, N., Tompkins, E., Adger, N. & Delaney, K. Vulnerability to Abrupt Climate Change in Europe (Tyndall Centre, 2005).

69 Link, P. M. & Tol, R. S. J. Possible economic impacts of a shutdown of the thermohaline circulation: an application of FUND. Port. Econ. J. 3, 99–114 (2004).

70 Schwartz, P. & Randall, D. An Abrupt Climate Change Scenario and Its Implications for United States National Security (Global Business Network, 2003).

71 Shearer, A. W. Whether the weather: comments on An Abrupt Climate Change Scenario and Its Implications for United States National Security. Futures 37, 445–463 (2005).

72 Stirling, A. in Negotiating Change: Perspectives in Environmental Social Science (eds Scoones, I., Leach, M. & Berkhout, F.) 33–76 (Edward Elgar, 2003).

73 Jackson, S. C. Parallel pursuit of near-term and long-term climate mitigation. Science 326, 526–527 (2009).

74 Lenton, T. M. & Vaughan, N. E. The radiative forcing potential of different climate geoengineering options. Atmos. Chem. Phys. 9, 5539–5561 (2009).

75 Huybrechts, P. & De Wolde, J. The dynamic response of the Greenland and Antarctic ice sheets to multiple-century climatic warming. J. Clim. 12, 2169–2188 (1999).

76 Patt, A. & Gwata, C. Effective seasonal climate forecast applications: examining constraints for subsistence farmers in Zimbabwe. Glob. Environ. Change 12, 185–195 (2002).

77 Kurz, W. A. et al. Mountain pine beetle and forest carbon feedback to climate change. Nature 452, 987–990 (2008).

78 Kurz, W. A., Stinson, G., Rampley, G. J., Dymond, C. C. & Neilson, E. T. Risk of natural disturbances makes future contribution of Canada's forests to the global carbon cycle highly uncertain. Proc. Natl Acad. Sci. USA 105, 1551–1555 (2008).

79 Contamin, R. & Ellison, A. M. Indicators of regime shifts in ecological systems: What do we need to know and when do we need to know it? Ecol. Appl. 19, 799–816 (2009).

80 Lenton, T. M. in The Future of the World's Climate (eds Henderson-Sellers, A. & McGuffie, K.) (Elsevier, in the press).