Projection of Climate Departure: Assessing Climate Change

Scientists at University of Hawai have projected the timing of climate departure from the present variabilities. First of all, let me explain to you what this means. The climate is changing at a very slow pace , thus the changes in ecological and social parameters due to climate change are extremely less when considered for a small time scale. However, when viewed at a large time scale, they appear to have changed a lot as does the climate. So, the scientists have tried to project/predict the time period till which the climate will change to such extremes which has not occurred in last 145 years. 

They presented an index for the time when the projected mean climate of a given location moves to a state continuously outside the bounds of historical variability under alternative greenhouse gas emissions scenarios. The historical variabilities they have considered in this study are from 1860 to 2005. So, the temperature conditions being assessed for a city when it hits the "climate departure" are such that the average temperature of the city's coolest year from then on is projected to be warmer than the average temperature of its hottest year between 1860 and 2005. 

This index has a global mean of 2069 (±18 years s.d.) for near-surface air temperature under an emissions stabilization scenario and 2047 (±14 years s.d.) under a ‘business-as-usual’ scenario. This means that if we stabilize the emissions, the climate departure for near-surface air temperature will occur in 2069, that is, 56 years from now (solid blue line in fig c); and in the case of continuing emissions at our present rate (which will increase with time) with no additional boundations on emissions, the climate departure will occur in 2047, that is, 34 years from now (solid red line in fig c).

a, b, Projected year when annual (a) or monthly (b) air temperature means move to a state continuously outside annual or monthly historical bounds, respectively.c, Absolute change in mean annual air temperature. (Results in a–c are based on RCP85.) d, Cumulative frequency of 100-km grid cells according to the projected timing of climate departure from recent variability for air temperature under two emissions scenarios (vertical lines indicate the median year). e, Scatter plot relating the grid cells from the map of absolute change (c) to the same grid cells from the map of projected timing of climate departure (a).
Source: http://www.nature.com/nature/journal/v502/n7470/full/nature12540.html

They also found out that the unprecedented climates will occur earliest in the tropics and among low-income countries, highlighting the vulnerability of global biodiversity and the limited governmental capacity to respond to the impacts of climate change. The study states, "The fact that the earliest climate departures occur in low-income countries further highlights an obvious disparity between those who benefit economically from the processes leading to climate change and those who will have to pay for most of the environmental and social costs."

They also emphasised on the emission control measures required by the developed countries as, "This suggests that any progress to decrease the rate of ongoing climate change will require a bigger commitment from developed countries to decrease their emissions but will also require more extensive funding of social and conservation programmes in developing countries to minimize the impacts of climate change."

Their study is of significance in terms of the urgency of mitigating greenhouse gas emissions if widespread changes in global biodiversity and human societies are to be prevented. 

Following is the image representing the year of climate departure of various cities for both emissions control measures scenario and business-as-usual scenario.

Climate Departure with carbon dioxide mitigation
Source: The Washington Post

Climate Departure without carbon dioxide mitigation
Source: The Washington Post

One of our Indian cities, Mumbai, as predicted will have a climate departure in 2034 (approx 20 years from now) without carbon dioxide emissions mitigation and 2051 with mitigation.

The study can be accessed here: http://www.nature.com/nature/journal/v502/n7470/full/nature12540.html

Journal: http://www.nature.com/nature/index.html