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Earth’s energy imbalance and climate change

July 29, 2015 | Comments: 0Author:

By Vladimir Đurđević, Institute of Meteorology, Faculty of Physics, University of Belgrade
vdj@ff.bg.ac.rs

Planet Earth is in energy imbalance. More energy is coming into the system than leaving it. It is a fact that can be measured, thanks to the many observations of the state of the climate system that we have today. Natural quasi-equilibrium state that existed for thousands of years has been disrupted during the one hundred years. The reason is the continuous increase in the concentration of carbon-dioxide and other greenhouse gases in the atmosphere, in the first place because of uncontrolled burning of fossil fuels. As a result of this, global average temperature is about 0.85°C higher than at the end of nineteenth century. In the middle of the twentieth century, when it first became clear what increased CO2 concentration can lead to, these changes were still insignificant and masked by natural variability. In the nineties, just as the prediction assumed, signals of changes in the system became visible and could be clearly separated from natural variations. Today, beside the increase in the global mean temperature we can observe many other changes in the different parts of planet Earth’s climate system. Northern ice cap is steadily reduced, sea level is constantly rising, and heat accumulated in oceans is on an upward trajectory, making oceans more acidic.

Natural quasi-equilibrium state that existed for thousands of years has been disrupted during the one hundred years. The reason is the continuous increase in the concentration of carbon-dioxide and other greenhouse gases in the atmosphere, in the first place because of uncontrolled burning of fossil fuels.

Danger from extremes

Our region of Southeastern Europe is also under pressure due to a changing climate. Current temperature increase is higher than the global average and it is close to 0.3°C per decade since the middle of the twentieth century. Occurrence of heat waves has almost doubled. The southern part of the region already faces a shortage in annual rainfall amounts. In the northern and central parts, even though there is no evidence of significant change in the annual accumulation of rain, there are more extremes. The problem with the climate change is not only in the change of long-term mean values, but also the change in the frequency and intensity of extremes. Many meteorological stations in region have recorded a statistically significant positive trend of daily accumulated precipitation that belongs to highest top 5%. On the other side, the region had several episodes of water shortage and drought since 2000. One of the most striking ones was the drought of 2012. These extreme events clearly show us that our society, despite continuous technological and engineering development, is still vulnerable and fragile in relation to these extreme events. More and stronger extremes mean more risk in our lives.

Current temperature increase for SEE region is higher than the global average and it is close to 0.3°C per decade since the middle of the twentieth century.

Old predictions were true

If we are clear about the facts and observed evidence, main question is how the future will look like. What is the future of continuing emissions of greenhouse gases and how will they affect the climate? The Intergovernmental Panel on Climate Change (IPCC) published a so-called supplementary report of the first assessment in 1992. It defined the range of possible scenarios of future greenhouse gases emissions, depending largely on how much fossil fuel will be used in the future, and after more than two decades, today we are able to verify these scenarios. First of all, our current emissions are within the range that has been assessed, and it can be considered a successful outcome for the IPCC. The bad news is that during the last twenty years we were on the upper limit of the possible range. In other words, at the global level, almost nothing has been done regarding the need for emissions reduction. If we stay on this pessimistic course the global temperature and sea level will continue to rise, ice cores will continue to shrink, dry regions will become drier and wet ones wetter. According to this pessimistic scenario, climate models predict the increase of annual mean temperature of about 4°C in our region by the end of this century in comparison to the middle of the twentieth century, with a reduction in annual precipitation of about 10%, but a more drastic one during summer moths. Some scenarios show decrease of up to 50% for summer season precipitation. This substantial shift in climate condition can have a more than serious impact on all socio- and eco-systems in our region.

According to this pessimistic scenario, climate models predict the increase of annual mean temperature of about 4°C in our region by the end of this century in comparison to the middle of the twentieth century, with a reduction in annual precipitation of about 10%, but a more drastic one during summer moths.

Carbon budget halved

If we want to minimize future risks and avoid unacceptable negative consequences, a global agreement is necessary as soon as possible. That is the reason why success of the 21st Conference of the Parties in Paris scheduled for December is crucial for our future. The agreement should provide mechanisms that will limit future emissions to levels that will not cause a rise in global average temperature of more than 2°C above pre-industrial levels. “Carbon budget” is a number that tells us the amount of carbon dioxide emissions we can emit while still having a 66% chance of limiting global temperature raise to this target. Accumulated emission since the start of industrial revolution, which gives us this chance to stay below a 2°C rise, is about 1,000 gigatonnes of carbon. Since the end of the nineteen century we already spent more than a half, with a constant increase in emissions per year. If we continue with the current trend in budget spending, we will reach the limit in about two decades. Also, all known coal, oil and natural gas reserves are three times bigger than needed to pass budget limit. Therefore, most of these reserves must stay below ground, if we really want to avoid increased risks from adverse effects of climate change that will be difficult to adapt. Even if we achieve this goal, adaptation seems unavoidable. Sadly, some systems will not be able to adapt, especially when we talk about eco-systems such as majority of coral reefs and habitats on mountain tops.

The energy sector should play a leading role in achieving this goal. It is already commonplace that this transformation should be seen as a development opportunity and not as a barrier for the sector. We will need international negotiations, agreements, regulations and limits at the last moment.

We must give a chance to the planet to reach energy balance once again, one that is not far from when modern society was developed. For the new balance, centuries will be required, due to the slow processes in the system such as ocean currents and ice caps melting, but the sooner we start, a balance will be more possible.

If we want to minimize future risks and avoid unacceptable negative consequences, a global agreement is necessary as soon as possible. That is the reason why success of the 21st Conference of the Parties in Paris scheduled for December is crucial for our future.

 Earth's energy imbalance and climate change

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Picture 1: Percentage change of total accumulated extreme daily precipitation for the period 2041–2070 with respect to 1971–2000, according to scenario RCP8.5 of Intergovernmental Panel on Climate Change. For days with extreme precipitation daily accumulation will be above threshold for the top 5% precipitation amounts in period 1971–2000. RCP8.5 assumes that concentration of greenhouse gasses will continue to increase. Green colour indicates extreme precipitation increase and brown indicates decrease. For the majority of the region projected increase is between 10% and 40%.

Data source: Orientgateproject.com;
Project partner: Republic Hydrometeorological Service of Serbia;
Model: NMMB.