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Climate inertia or climate change inertia is the phenomenon by which a planet's climate system shows a resistance or slowness to deviate away from a given dynamical system. It can accompany stability theory and other effects of feedback within , and includes the inertia exhibited by physical movements of matter and exchanges of energy. The term is a colloquialism used to encompass and loosely describe a set of interactions that extend the timescales around climate sensitivity. Inertia has been associated with the drivers of, and the responses to, climate change.
Increasing fossil fuels carbon emissions are a primary inertial driver of change to Earth's climate during recent decades, and have risen along with the collective socioeconomic inertia of its 8 billion human inhabitants. Many system components have exhibited inertial responses to this driver, also known as a climate forcing. The rate of rise in global surface temperature (GST) has especially been resisted by 1) the thermal inertia of the planet's surface, primarily its ocean, and 2) inertial behavior within its carbon cycle feedback. Various other biogeochemical feedbacks have contributed further resiliency. Energy stored in the ocean following the inertial responses principally determines near-term irreversible change known as climate commitment.
Earth's inertial responses are important because they provide the planet's diversity of life and its human civilization further time to adapt to an acceptable degree of planetary change. However, unadaptable change like that accompanying some tipping points may only be avoidable with early understanding and mitigation of the risk of such dangerous outcomes. This is because inertia also delays much surface warming unless and until action is taken to rapidly reduce emissions. An aim of Integrated assessment modelling, summarized for example as Shared Socioeconomic Pathways (SSP), is to explore Earth system risks that accompany large inertia and uncertainty in the trajectory of human drivers of change.
| + Response times to climate forcing
! Earth System Component !! Time Constant (years) !! Response Modes |
| EC, WC |
| CC |
| EC, WC, CC |
| EC, CC |
| EC, WC, CC |
| CC |
| EC, WC |
| EC, WC |
| EC, WC |
| CC |
| WC, CC |
The paleoclimate record shows that Earth's climate system has evolved along various pathways and with multiple timescales. Its relatively stable states which can persist for many millennia have been interrupted by short to long transitional periods of relative instability. Studies of climate sensitivity and inertia are concerned with quantifying the most basic manner in which a sustained forcing perturbation will cause the system to deviate within or initially away from its relatively stable state of the present Holocene epoch.
"" are useful metrics for summarizing the first-order (linear) impacts of the various inertial phenomena within both simple and complex systems. They quantify the time after which 63% of a full output response occurs following the step change of an input. They are observed from data or can be estimated from numerical simulation or a lumped system analysis. In climate science these methods can be applied to Earth's energy cycle, water cycle, carbon cycle and elsewhere. For example, heat transport and heat capacity in the ocean, cryosphere, land and atmosphere are elements within a lumped thermal analysis. Response times to radiative forcing via the atmosphere typically increase with depth below the surface.
Inertial time constants indicate a base rate for forced changes, but lengthy values provide no guarantee of long-term system evolution along a smooth pathway. Numerous higher-order tipping elements having various trigger thresholds and transition timescales have been identified within Earth's present state. Such events might precipitate a nonlinear system rearrangement of internal energy flows along with more rapid shifts in climate and/or other systems at regional to global scale.
ECS response time is proportional to ECS and is principally regulated by the thermal inertia of the uppermost mixed layer and adjacent lower ocean layers. Main time constants fitted to the results from climate models have ranged from a few decades when ECS is low, to as long as a century when ECS is high. A portion of the variation between estimates arises from different treatments of heat transport into the deep ocean.
Permafrost also takes longer to respond to a warming planet because of thermal inertia, due to ice rich materials and permafrost thickness.
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