. Historical warming forms a sequence of steady-state regimes punctuated by abrupt shifts. These ... more . Historical warming forms a sequence of steady-state regimes punctuated by abrupt shifts. These changes are regulated by a heat engine spanning the tropical Pacific Ocean teleconnected to a broader climate network. The eastern-central Pacific maintains steady-state conditions, delivering heat to the Western Pacific warm pool. They form a heat pump with heat moving from the cold to the warm reservoir, sustained by kinetic energy. The two reservoirs exchange heat on a range of timescales, with oscillatory behaviour that intensifies under forcing. The heat engine is part of a network of oscillations and circulation interacting on a range of timescales. The process is self-regulating: steady-state regimes persist until they become unstable due to an over- or under-supply of heat for dissipation, shifting warmer or cooler to a new stable state. Pre-industrial climate was in free mode, characterised by a loosely-coupled ocean-atmosphere with limited circulation, moving into forced mode in the latter 20th century, characterised by tighter coupling and stronger circulation through the tropical Pacific with more active teleconnections globally. Continued forcing produces a stepladder-like pattern of warming. Most shifts coincide with phase changes in decadal oscillations, switching from slower to faster modes of dissipation. El Niño events combine with regime shifts to propagate heat from the oceans to land and from the tropics to higher latitudes. The most recent shift commenced in the warm pool in December 2012, ending the so-called hiatus (1997–2013), global mean surface temperatures warming abruptly by ~0.25 °C in 2014–15.
The uncertainty surrounding climate change is a major obstacle facing the sustainable management ... more The uncertainty surrounding climate change is a major obstacle facing the sustainable management of water resources in Australia. We describe a modelling system built to analyse the risk of climate change using results obtained from water resource modelling of the Macquarie River catchment in NSW. Scenarios of climate change in 2030 and 2070, selected from the outputs of nine climate
The problem solution framework was developed by actively working with researchers and climate cha... more The problem solution framework was developed by actively working with researchers and climate change practitioners in Australia over a number of years to assist practitioners in making sense of the information they received and how to apply it in their context. It focuses on the recognition that dealing with a problem and solution involves very different psychology and outlines the change over point between the two phases and examines the tools, methods and thinking frameworks needed for different parts of this process. Topics in the guide include: Understanding adaptation The problem solution process framework Innovation and adaptation Adaptation communication Developing and integrating new knowledge Managing change
In an effort to increase the livability of its cities, public agencies in Australia are investing... more In an effort to increase the livability of its cities, public agencies in Australia are investing in green infrastructure to improve public health, reduce heat island effects and transition toward water sensitive urban design. In this paper, we present a simple and replicable approach to building a business case for green infrastructure. This approach requires much less time and resources compared to other methods for estimating the social and economic returns to society from such investments. It is a pragmatic, reasonably comprehensive approach that includes socio-demographic profile of potential users and catchment analysis to assess the economic value of community benefits of the investment. The approach has been applied to a case study area in the City of Brimbank, a western suburb of Greater Melbourne. We find that subject to a set of assumptions, a reasonable business case can be made. We estimate potential public benefits of avoided health costs of about AU$75,049 per annum a...
For the past decade, climate research has responded to challenges that atmospheric warming either... more For the past decade, climate research has responded to challenges that atmospheric warming either slowed or stopped in 1998. Of the responses, the hypothesis least examined is whether climate change and variability are interacting to produce step‐like regime changes. Step‐change analysis identifies a step of 0.32±0.01°C in five records of global mean surface temperature (GMST) in 1997, followed by a trend to 2014 ranging between 0.06°C decade‐1 and 0.11°C decade‐1. Thirty‐nine of 45 zonal, hemispheric and global records register a step change over the period 1996–98. The difference between one trend and the next across a step change provides a minimum estimate of the shift. The average global shift in 1997 is 0.16±0.01°C, around 50% of the average step. For the northern hemisphere mid‐latitudes, steps/shifts measure 0.43°C/0.44°C, indicating no trend. Of the 107 members of a multi‐model ensemble (MME) from the CMIP5 RCP4.5 archive, 58 register a step change in 1996–98, averaging 0.41°C (0.22°C to 0.73°C). The following step averaging 0.31°C (0.16°C to 0.52°C) occurs after a period of 7 to 26 years. The 1996–98 step is uncorrelated with model equilibrium climate sensitivity (ECS) but the following step change is highly correlated (0.58). Step‐change analysis in both observations and models suggests that rapid changes punctuate more stable regimes forming a step‐ladder like progression. If the current spike in temperature from the 2014–16 El Niño event represents the early stages of a step change similar to 1997–98, the world may be entering a regime of new and heightened climate risk
This paper takes as its starting point the debate surrounding whether global warming after 1998 i... more This paper takes as its starting point the debate surrounding whether global warming after 1998 is a routine part of a gradual, long‐term trend or whether discontinuities in the temperature record either show the theory is wrong or that climate risks are overstated. It argues the main scientific defence, though correct, is scientifically weak and open to criticism because it sidesteps the role of nonlinearity in the warming process. Additionally, the distinction between short‐ and long‐term trends is subjective and depends on the method used to create that distinction. The paper applies three areas of the philosophy of science to reconcile the situation: (1) it uses the structure of scientific research programmes to identify the key core and auxiliary global warming theory in order to frame a more robust scientific response; (2) it addresses theory falsification and confirmation to identify spurious arguments aimed at discounting global warming theory based on dogmatic empiricism and (3) it investigates the potential for severe testing to investigate scientific hypotheses supporting gradual trend‐like and nonlinear steplike warming: the two simplest models of change. The results (undertaken in another paper) suggest that each side is both right and wrong. Warming is largely steplike, caused by interactions between climate change and variability confirming the stepladder–escalator model, but in a manner consistent with global warming theory. Over many decades, these steps integrate into a complex trend, so the critics are wrong in their interpretations of what these steps mean. Communicating complex and simple trends is more theoretically robust than communicating short‐ and long‐term trends. If climate change follows a nonlinear pathway on decadal timescales, methods for detection and attribution, decadal prediction, the characterisation of risk and their communication all need to change. Scientific narratives need to move on from the existing gradualist narrative to those that addresses complexity and communicate uncertainty more effectively.
Interactions between externally‐forced and internally‐generated climate variations on decadal tim... more Interactions between externally‐forced and internally‐generated climate variations on decadal timescales is a major determinant of changing climate risk. Severe testing is applied to observed global and regional surface and satellite temperatures and modelled surface temperatures to determine whether these interactions are independent, as in the traditional signal‐to‐noise model, or whether they interact, resulting in steplike warming. The multi‐step bivariate test is used to detect step changes in temperature data. The resulting data are then subject to six tests designed to show strong differences between the two statistical hypotheses, hstep and htrend: (1) Since the mid‐20th century, most of the observed warming has taken place in four events: in 1979/80 and 1997/98 at the global scale, 1988/89 in the northern hemisphere and 1968/70 in the southern hemisphere. Temperature is more steplike than trend‐like on a regional basis. Satellite temperature is more steplike than surface temperature. Warming from internal trends is less than 40% of the total for four of five global records tested (1880–2013/14). (2) Correlations between step‐change frequency in models and observations (1880–2005), are 0.32 (CMIP3) and 0.34 (CMIP5). For the period 1950–2005, grouping selected events (1963/64, 1968–70, 1976/77, 1979/80, 1987/88 and 1996–98), correlation increases to 0.78. (3) Steps and shifts (steps minus internal trends) from a 107‐member climate model ensemble 2006–2095 explain total warming and equilibrium climate sensitivity better than internal trends. (4) In three regions tested, the change between stationary and non‐stationary temperatures is steplike and attributable to external forcing. (5) Steplike changes are also present in tide gauge observations, rainfall, ocean heat content, forest fire danger index and related variables. (6) Across a selection of tests, a simple stepladder model better represents the internal structures of warming than a simple trend – strong evidence that the climate system is exhibiting complex system behaviour on decadal timescales. This model indicates that in situ warming of the atmosphere does not occur; instead, a store and‐release mechanism from the ocean to the atmosphere is proposed. It is physically plausible and theoretically sound. The presence of steplike – rather than gradual – warming is important information for characterising and managing future climate risk.
This paper is one of a series aiming to reconcile the scientific understanding of how external fo... more This paper is one of a series aiming to reconcile the scientific understanding of how external forcing and internal variability interact on decadal timescales. These papers examine the theoretical basis of, evidence for, and the history and philosophy of the scientific effort to understand how the climate changes under gradual radiative forcing. Does the change follow the gradual forcing pathway, or is does the climate system respond nonlinearly? This paper investigates the current narratives and hypotheses describing how the relationship between externally‐forced and internally‐generated climate variations are viewed. Two hypotheses describe how these processes combine: anthropogenic climate change is independent of natural climate variability (H1), or they interact (H2). In H1, anthropogenic climate change is gradual, its rate of change being mediated by climate variability. In H2, climate has a nonlinear response, arising from the interaction between the external and internal components of the climate system. Current methods to analyse and communicate climate change overwhelmingly self‐select H1. This has resulted in a scientific narrative of gradual change that dominates discourse within climate science. This imbalance is not supported by current theoretical understanding, which considers either H1 or H2 as being possible, and evidence of step‐like changes in climate, which supports H2.
. Historical warming forms a sequence of steady-state regimes punctuated by abrupt shifts. These ... more . Historical warming forms a sequence of steady-state regimes punctuated by abrupt shifts. These changes are regulated by a heat engine spanning the tropical Pacific Ocean teleconnected to a broader climate network. The eastern-central Pacific maintains steady-state conditions, delivering heat to the Western Pacific warm pool. They form a heat pump with heat moving from the cold to the warm reservoir, sustained by kinetic energy. The two reservoirs exchange heat on a range of timescales, with oscillatory behaviour that intensifies under forcing. The heat engine is part of a network of oscillations and circulation interacting on a range of timescales. The process is self-regulating: steady-state regimes persist until they become unstable due to an over- or under-supply of heat for dissipation, shifting warmer or cooler to a new stable state. Pre-industrial climate was in free mode, characterised by a loosely-coupled ocean-atmosphere with limited circulation, moving into forced mode in the latter 20th century, characterised by tighter coupling and stronger circulation through the tropical Pacific with more active teleconnections globally. Continued forcing produces a stepladder-like pattern of warming. Most shifts coincide with phase changes in decadal oscillations, switching from slower to faster modes of dissipation. El Niño events combine with regime shifts to propagate heat from the oceans to land and from the tropics to higher latitudes. The most recent shift commenced in the warm pool in December 2012, ending the so-called hiatus (1997–2013), global mean surface temperatures warming abruptly by ~0.25 °C in 2014–15.
The uncertainty surrounding climate change is a major obstacle facing the sustainable management ... more The uncertainty surrounding climate change is a major obstacle facing the sustainable management of water resources in Australia. We describe a modelling system built to analyse the risk of climate change using results obtained from water resource modelling of the Macquarie River catchment in NSW. Scenarios of climate change in 2030 and 2070, selected from the outputs of nine climate
The problem solution framework was developed by actively working with researchers and climate cha... more The problem solution framework was developed by actively working with researchers and climate change practitioners in Australia over a number of years to assist practitioners in making sense of the information they received and how to apply it in their context. It focuses on the recognition that dealing with a problem and solution involves very different psychology and outlines the change over point between the two phases and examines the tools, methods and thinking frameworks needed for different parts of this process. Topics in the guide include: Understanding adaptation The problem solution process framework Innovation and adaptation Adaptation communication Developing and integrating new knowledge Managing change
In an effort to increase the livability of its cities, public agencies in Australia are investing... more In an effort to increase the livability of its cities, public agencies in Australia are investing in green infrastructure to improve public health, reduce heat island effects and transition toward water sensitive urban design. In this paper, we present a simple and replicable approach to building a business case for green infrastructure. This approach requires much less time and resources compared to other methods for estimating the social and economic returns to society from such investments. It is a pragmatic, reasonably comprehensive approach that includes socio-demographic profile of potential users and catchment analysis to assess the economic value of community benefits of the investment. The approach has been applied to a case study area in the City of Brimbank, a western suburb of Greater Melbourne. We find that subject to a set of assumptions, a reasonable business case can be made. We estimate potential public benefits of avoided health costs of about AU$75,049 per annum a...
For the past decade, climate research has responded to challenges that atmospheric warming either... more For the past decade, climate research has responded to challenges that atmospheric warming either slowed or stopped in 1998. Of the responses, the hypothesis least examined is whether climate change and variability are interacting to produce step‐like regime changes. Step‐change analysis identifies a step of 0.32±0.01°C in five records of global mean surface temperature (GMST) in 1997, followed by a trend to 2014 ranging between 0.06°C decade‐1 and 0.11°C decade‐1. Thirty‐nine of 45 zonal, hemispheric and global records register a step change over the period 1996–98. The difference between one trend and the next across a step change provides a minimum estimate of the shift. The average global shift in 1997 is 0.16±0.01°C, around 50% of the average step. For the northern hemisphere mid‐latitudes, steps/shifts measure 0.43°C/0.44°C, indicating no trend. Of the 107 members of a multi‐model ensemble (MME) from the CMIP5 RCP4.5 archive, 58 register a step change in 1996–98, averaging 0.41°C (0.22°C to 0.73°C). The following step averaging 0.31°C (0.16°C to 0.52°C) occurs after a period of 7 to 26 years. The 1996–98 step is uncorrelated with model equilibrium climate sensitivity (ECS) but the following step change is highly correlated (0.58). Step‐change analysis in both observations and models suggests that rapid changes punctuate more stable regimes forming a step‐ladder like progression. If the current spike in temperature from the 2014–16 El Niño event represents the early stages of a step change similar to 1997–98, the world may be entering a regime of new and heightened climate risk
This paper takes as its starting point the debate surrounding whether global warming after 1998 i... more This paper takes as its starting point the debate surrounding whether global warming after 1998 is a routine part of a gradual, long‐term trend or whether discontinuities in the temperature record either show the theory is wrong or that climate risks are overstated. It argues the main scientific defence, though correct, is scientifically weak and open to criticism because it sidesteps the role of nonlinearity in the warming process. Additionally, the distinction between short‐ and long‐term trends is subjective and depends on the method used to create that distinction. The paper applies three areas of the philosophy of science to reconcile the situation: (1) it uses the structure of scientific research programmes to identify the key core and auxiliary global warming theory in order to frame a more robust scientific response; (2) it addresses theory falsification and confirmation to identify spurious arguments aimed at discounting global warming theory based on dogmatic empiricism and (3) it investigates the potential for severe testing to investigate scientific hypotheses supporting gradual trend‐like and nonlinear steplike warming: the two simplest models of change. The results (undertaken in another paper) suggest that each side is both right and wrong. Warming is largely steplike, caused by interactions between climate change and variability confirming the stepladder–escalator model, but in a manner consistent with global warming theory. Over many decades, these steps integrate into a complex trend, so the critics are wrong in their interpretations of what these steps mean. Communicating complex and simple trends is more theoretically robust than communicating short‐ and long‐term trends. If climate change follows a nonlinear pathway on decadal timescales, methods for detection and attribution, decadal prediction, the characterisation of risk and their communication all need to change. Scientific narratives need to move on from the existing gradualist narrative to those that addresses complexity and communicate uncertainty more effectively.
Interactions between externally‐forced and internally‐generated climate variations on decadal tim... more Interactions between externally‐forced and internally‐generated climate variations on decadal timescales is a major determinant of changing climate risk. Severe testing is applied to observed global and regional surface and satellite temperatures and modelled surface temperatures to determine whether these interactions are independent, as in the traditional signal‐to‐noise model, or whether they interact, resulting in steplike warming. The multi‐step bivariate test is used to detect step changes in temperature data. The resulting data are then subject to six tests designed to show strong differences between the two statistical hypotheses, hstep and htrend: (1) Since the mid‐20th century, most of the observed warming has taken place in four events: in 1979/80 and 1997/98 at the global scale, 1988/89 in the northern hemisphere and 1968/70 in the southern hemisphere. Temperature is more steplike than trend‐like on a regional basis. Satellite temperature is more steplike than surface temperature. Warming from internal trends is less than 40% of the total for four of five global records tested (1880–2013/14). (2) Correlations between step‐change frequency in models and observations (1880–2005), are 0.32 (CMIP3) and 0.34 (CMIP5). For the period 1950–2005, grouping selected events (1963/64, 1968–70, 1976/77, 1979/80, 1987/88 and 1996–98), correlation increases to 0.78. (3) Steps and shifts (steps minus internal trends) from a 107‐member climate model ensemble 2006–2095 explain total warming and equilibrium climate sensitivity better than internal trends. (4) In three regions tested, the change between stationary and non‐stationary temperatures is steplike and attributable to external forcing. (5) Steplike changes are also present in tide gauge observations, rainfall, ocean heat content, forest fire danger index and related variables. (6) Across a selection of tests, a simple stepladder model better represents the internal structures of warming than a simple trend – strong evidence that the climate system is exhibiting complex system behaviour on decadal timescales. This model indicates that in situ warming of the atmosphere does not occur; instead, a store and‐release mechanism from the ocean to the atmosphere is proposed. It is physically plausible and theoretically sound. The presence of steplike – rather than gradual – warming is important information for characterising and managing future climate risk.
This paper is one of a series aiming to reconcile the scientific understanding of how external fo... more This paper is one of a series aiming to reconcile the scientific understanding of how external forcing and internal variability interact on decadal timescales. These papers examine the theoretical basis of, evidence for, and the history and philosophy of the scientific effort to understand how the climate changes under gradual radiative forcing. Does the change follow the gradual forcing pathway, or is does the climate system respond nonlinearly? This paper investigates the current narratives and hypotheses describing how the relationship between externally‐forced and internally‐generated climate variations are viewed. Two hypotheses describe how these processes combine: anthropogenic climate change is independent of natural climate variability (H1), or they interact (H2). In H1, anthropogenic climate change is gradual, its rate of change being mediated by climate variability. In H2, climate has a nonlinear response, arising from the interaction between the external and internal components of the climate system. Current methods to analyse and communicate climate change overwhelmingly self‐select H1. This has resulted in a scientific narrative of gradual change that dominates discourse within climate science. This imbalance is not supported by current theoretical understanding, which considers either H1 or H2 as being possible, and evidence of step‐like changes in climate, which supports H2.
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Papers by Roger Jones
ranging between 0.06°C decade‐1 and 0.11°C decade‐1. Thirty‐nine of 45 zonal, hemispheric and global records register a step change over the period 1996–98. The difference between one trend and the next
across a step change provides a minimum estimate of the shift. The average global shift in 1997 is 0.16±0.01°C, around 50% of the average step. For the northern hemisphere mid‐latitudes, steps/shifts
measure 0.43°C/0.44°C, indicating no trend. Of the 107 members of a multi‐model ensemble (MME) from the CMIP5 RCP4.5 archive, 58 register a step change in 1996–98, averaging 0.41°C (0.22°C to 0.73°C). The following step averaging 0.31°C (0.16°C to 0.52°C) occurs after a period of 7 to 26 years. The 1996–98 step is uncorrelated with model equilibrium climate sensitivity (ECS) but the following step change is highly correlated (0.58). Step‐change analysis in both observations and models suggests that rapid changes punctuate more stable regimes forming a step‐ladder like progression. If the current spike in temperature from the 2014–16 El Niño event represents the early stages of a step change similar to 1997–98, the world may be entering a regime of new and heightened climate risk
scientifically weak and open to criticism because it sidesteps the role of nonlinearity in the warming process. Additionally, the distinction between short‐ and long‐term trends is subjective and depends on the method used to create that distinction. The paper applies three areas of the philosophy of science to reconcile the situation: (1) it uses the structure of scientific research programmes to identify the key core and auxiliary global warming theory in order to frame a more robust scientific response; (2) it addresses theory falsification and confirmation to identify spurious arguments aimed at discounting global warming theory based on dogmatic empiricism and (3) it investigates the potential for severe testing to investigate scientific hypotheses supporting gradual trend‐like and nonlinear steplike warming: the two simplest models of change. The results (undertaken in another paper) suggest that each side is both right and wrong. Warming is largely steplike, caused by interactions between climate change and variability confirming the stepladder–escalator model, but in a manner consistent with global warming theory. Over many decades, these steps
integrate into a complex trend, so the critics are wrong in their interpretations of what these steps mean. Communicating complex and simple trends is more theoretically robust than communicating short‐ and long‐term trends. If climate change follows a nonlinear pathway on decadal timescales, methods for
detection and attribution, decadal prediction, the characterisation of risk and their communication all need to change. Scientific narratives need to move on from the existing gradualist narrative to those that addresses complexity and communicate uncertainty more effectively.
surface and satellite temperatures and modelled surface temperatures to determine whether these interactions are independent, as in the traditional signal‐to‐noise model, or whether they interact, resulting
in steplike warming. The multi‐step bivariate test is used to detect step changes in temperature data. The resulting data are then subject to six tests designed to show strong differences between the two statistical
hypotheses, hstep and htrend: (1) Since the mid‐20th century, most of the observed warming has taken place in four events: in 1979/80 and 1997/98 at the global scale, 1988/89 in the northern hemisphere and 1968/70 in the southern hemisphere. Temperature is more steplike than trend‐like on a regional basis. Satellite temperature is more steplike than surface temperature. Warming from internal trends is less than 40% of
the total for four of five global records tested (1880–2013/14). (2) Correlations between step‐change frequency in models and observations (1880–2005), are 0.32 (CMIP3) and 0.34 (CMIP5). For the period
1950–2005, grouping selected events (1963/64, 1968–70, 1976/77, 1979/80, 1987/88 and 1996–98),
correlation increases to 0.78. (3) Steps and shifts (steps minus internal trends) from a 107‐member climate model ensemble 2006–2095 explain total warming and equilibrium climate sensitivity better than internal trends. (4) In three regions tested, the change between stationary and non‐stationary temperatures is steplike and attributable to external forcing. (5) Steplike changes are also present in tide gauge
observations, rainfall, ocean heat content, forest fire danger index and related variables. (6) Across a selection of tests, a simple stepladder model better represents the internal structures of warming than a
simple trend – strong evidence that the climate system is exhibiting complex system behaviour on decadal timescales. This model indicates that in situ warming of the atmosphere does not occur; instead, a store and‐release mechanism from the ocean to the atmosphere is proposed. It is physically plausible and theoretically sound. The presence of steplike – rather than gradual – warming is important information for
characterising and managing future climate risk.
change being mediated by climate variability. In H2, climate has a nonlinear response, arising from the interaction between the external and internal components of the climate system. Current methods to
analyse and communicate climate change overwhelmingly self‐select H1. This has resulted in a scientific narrative of gradual change that dominates discourse within climate science. This imbalance is not
supported by current theoretical understanding, which considers either H1 or H2 as being possible, and evidence of step‐like changes in climate, which supports H2.
ranging between 0.06°C decade‐1 and 0.11°C decade‐1. Thirty‐nine of 45 zonal, hemispheric and global records register a step change over the period 1996–98. The difference between one trend and the next
across a step change provides a minimum estimate of the shift. The average global shift in 1997 is 0.16±0.01°C, around 50% of the average step. For the northern hemisphere mid‐latitudes, steps/shifts
measure 0.43°C/0.44°C, indicating no trend. Of the 107 members of a multi‐model ensemble (MME) from the CMIP5 RCP4.5 archive, 58 register a step change in 1996–98, averaging 0.41°C (0.22°C to 0.73°C). The following step averaging 0.31°C (0.16°C to 0.52°C) occurs after a period of 7 to 26 years. The 1996–98 step is uncorrelated with model equilibrium climate sensitivity (ECS) but the following step change is highly correlated (0.58). Step‐change analysis in both observations and models suggests that rapid changes punctuate more stable regimes forming a step‐ladder like progression. If the current spike in temperature from the 2014–16 El Niño event represents the early stages of a step change similar to 1997–98, the world may be entering a regime of new and heightened climate risk
scientifically weak and open to criticism because it sidesteps the role of nonlinearity in the warming process. Additionally, the distinction between short‐ and long‐term trends is subjective and depends on the method used to create that distinction. The paper applies three areas of the philosophy of science to reconcile the situation: (1) it uses the structure of scientific research programmes to identify the key core and auxiliary global warming theory in order to frame a more robust scientific response; (2) it addresses theory falsification and confirmation to identify spurious arguments aimed at discounting global warming theory based on dogmatic empiricism and (3) it investigates the potential for severe testing to investigate scientific hypotheses supporting gradual trend‐like and nonlinear steplike warming: the two simplest models of change. The results (undertaken in another paper) suggest that each side is both right and wrong. Warming is largely steplike, caused by interactions between climate change and variability confirming the stepladder–escalator model, but in a manner consistent with global warming theory. Over many decades, these steps
integrate into a complex trend, so the critics are wrong in their interpretations of what these steps mean. Communicating complex and simple trends is more theoretically robust than communicating short‐ and long‐term trends. If climate change follows a nonlinear pathway on decadal timescales, methods for
detection and attribution, decadal prediction, the characterisation of risk and their communication all need to change. Scientific narratives need to move on from the existing gradualist narrative to those that addresses complexity and communicate uncertainty more effectively.
surface and satellite temperatures and modelled surface temperatures to determine whether these interactions are independent, as in the traditional signal‐to‐noise model, or whether they interact, resulting
in steplike warming. The multi‐step bivariate test is used to detect step changes in temperature data. The resulting data are then subject to six tests designed to show strong differences between the two statistical
hypotheses, hstep and htrend: (1) Since the mid‐20th century, most of the observed warming has taken place in four events: in 1979/80 and 1997/98 at the global scale, 1988/89 in the northern hemisphere and 1968/70 in the southern hemisphere. Temperature is more steplike than trend‐like on a regional basis. Satellite temperature is more steplike than surface temperature. Warming from internal trends is less than 40% of
the total for four of five global records tested (1880–2013/14). (2) Correlations between step‐change frequency in models and observations (1880–2005), are 0.32 (CMIP3) and 0.34 (CMIP5). For the period
1950–2005, grouping selected events (1963/64, 1968–70, 1976/77, 1979/80, 1987/88 and 1996–98),
correlation increases to 0.78. (3) Steps and shifts (steps minus internal trends) from a 107‐member climate model ensemble 2006–2095 explain total warming and equilibrium climate sensitivity better than internal trends. (4) In three regions tested, the change between stationary and non‐stationary temperatures is steplike and attributable to external forcing. (5) Steplike changes are also present in tide gauge
observations, rainfall, ocean heat content, forest fire danger index and related variables. (6) Across a selection of tests, a simple stepladder model better represents the internal structures of warming than a
simple trend – strong evidence that the climate system is exhibiting complex system behaviour on decadal timescales. This model indicates that in situ warming of the atmosphere does not occur; instead, a store and‐release mechanism from the ocean to the atmosphere is proposed. It is physically plausible and theoretically sound. The presence of steplike – rather than gradual – warming is important information for
characterising and managing future climate risk.
change being mediated by climate variability. In H2, climate has a nonlinear response, arising from the interaction between the external and internal components of the climate system. Current methods to
analyse and communicate climate change overwhelmingly self‐select H1. This has resulted in a scientific narrative of gradual change that dominates discourse within climate science. This imbalance is not
supported by current theoretical understanding, which considers either H1 or H2 as being possible, and evidence of step‐like changes in climate, which supports H2.