Climate sensitivity and how close are we to dangerous anthropogenic interference in climate change?

Winters are shorter and temperature fluctuations between seasons are more extreme. More importantly, it has been scientifically proven that Earth is warming as measured by average surface temperatures. With a warming trend that is unlikely to be abated, significant changes will occur in atmospheric circulation and temperature resultant from a progressive increase in average carbon dioxide concentration. Climbing above 400 parts per million by volume (ppmv), carbon dioxide concentration in air has increased by an average of 2 ppmv a year due to emissions from fossil fuel combustion for electricity generation and industrial activity.


Hence, climate change is real and is likely to manifest in a variety of effects, each of which with severe consequences to the environment; for example, rise in sea levels, more frequent droughts, desertification, and changes in rainfall and seasonal patterns around the world. But, what is the anticipated timescale on which the above effects of climate change would present themselves? Such a question is of importance in understanding the dynamics of climate change, and more importantly, the timeline on which humanity can plan and implement measures for mitigating more severe aspects of climate change such as coastal erosion and the need for mass population relocation in the face of encroachment of low lying coastal cities by the sea.


But, are we able to model the way in which the Earth’s average temperature would rise in the face of a specific set of assumptions such as a representative emission and concentration profile, changing climate sensitivity factor, as well as efforts at carbon capture and sequestration (CCS)? The answer is yes and is increasingly sophisticated. Specifically, advanced computational methods, applied at the supercomputer level, is used in modeling changes in temperature and other climatic parameters for understanding the effect of different factors in determining the evolution of temperature profile at different parts of the world in the near, medium and far future. While climate prediction is fairly accurate in the near and medium term, long range projections of climatic evolution is still fraught with difficulties. But with improvement in estimating critical parameters in models, medium and long range prediction of temperature rise and rainfall patterns is increasingly more in sync with reality.


An important concept in understanding how fast or slow temperature would rise is the climate sensitivity factor. Specifically, climate sensitivity factor refers to the predicted rise in temperature engendered by a doubling of carbon dioxide concentration in the atmosphere. Therefore, considering that a doubling of carbon dioxide concentration would likely push the Earth’s climate change to the point of inducing dangerous anthropogenic interference, which is a state of the Earth’s climate where the level of carbon dioxide in the atmosphere has resulted in uncontrolled positive feedback loops with respect to temperature rise. Such a snowballing effect would push the planet, which was once habitable, to a state more akin to that in present day Venus, where high levels of carbon dioxide create a severe greenhouse effect that boiled off all surface liquid water.


Though fairly straightforward conceptually, estimation of climate sensitivity is an art form and large variation in the parameter exists in the scientific literature. Depending on the assumptions of how water vapor from enhanced evaporation (due to temperature rise) traps heat, as well as amount of cloud formation, the speed at which temperature rise with doubling of carbon dioxide concentration differs. But, why is understanding the extent of temperature rise with a doubling of carbon dioxide concentration in the atmosphere important? Fundamentally, the question provides a useful and relevant framework for understanding climate change: in essence, in opting a worse-case scenario for readout, climate sensitivity illuminates how far the Earth’s climate system is from disaster resulting from increasingly rapid increase in atmospheric carbon dioxide concentration.


Thus, what is a relevant reference point for understanding the effects and fundamental principles underlying the concept of dangerous climate change? The most often used and accepted concept in the climate change research community is dangerous anthropogenic interference (DAI). Specifically, dangerous anthropogenic interference refers to the possible runaway climate change induced in the Earth’s atmospheric and oceanic circulation system by levels of atmospheric carbon dioxide that results in a more than 2 oC rise in average surface temperature beyond that of the preindustrial era, circa, 1750.


Given that about 0.8 oC rise in average surface temperatures as compared to the preindustrial age has been realized, is it possible to measure the extent at which we are from dangerous anthropogenic interference via the difference between temperature rise observed and the noted value that would help keep the Earth’s climate system away from an unstable equilibrium? The answer is no, as there must be a holistic assessment of how far the present environment is from a potentially irreversible state of climatic fluctuations through a range of parameters and temperature evolution trajectories. Such an understanding could only be obtained from complex climate modeling studies as the sought after point of interest (i.e., present state of climate and future unsafe state of climate) are, mathematically and graphically, on a multidimensional graph which is incomprehensible without heavy abstraction.


Hence, how far is the human race from a state of climate where there could be likely irreversible changes to Earth’s climate system due to elevated carbon dioxide concentration in the atmosphere that cross a threshold? According to the best available climate models, the temperature rise that could potentiate dangerous anthropogenic interference in the climate system is 2 oC, where currently, there is observed 0.8 oC rise in temperature above preindustrial levels, the same reference for measurement. However, is there an alternative way for measuring the distance from which we are on a trajectory leading to irreversible and dangerous climate change that could not be effectively abated with current and anticipated future technologies? One yardstick is carbon inventory.


Used in measuring the relative extent at which various nations differ in emissions inventory that would still allow them to remain compliant with the 2015 Paris Agreement on climate change, carbon inventory is an interesting concept that put concrete and accessible numbers to a problem which hitherto has been beset with uncertainty. Though facing challenges in understanding the carbon budget that could keep Earth’s from dangerous climate change as well as the fossil fuels (tapped and untapped) that we have, the most important question of what is the level of carbon in the atmosphere that would keep the planet away from irreversible climate change as well as the present amount in the air. This affords a difference that could be translated, with some margin of error, into the amount of fossil fuel that we could use to power our economies, given that the cost margin of renewable energy remains higher than fossil fuel. Translated into numbers, the essence of the message is that we need to speed up efforts to develop renewable energy, or develop more sophisticated and efficient carbon capture and sequestration technologies if we are to stay on the current emissions trajectory without inducing irreversible climate change.


Category: climate change,

Tags: carbon budget, emissions inventory, dangerous anthropogenic interference, carbon dioxide, methane, climate change, global warming,






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