Market Forces

How renewables, natural gas and flat demand led to a drop in CO2 emissions from the US power sector

New state-by-state research shows significant reductions across the country from 2005-2015

 Decarbonizing the power sector in the United States will be critical to achieving the goal of a 100% clean economy by 2050 – especially since reaching “net-zero” greenhouse gas emissions across the economy means that other energy-using sectors such as buildings and transport will increasingly need to be electrified, switching away from direct fossil fuel use and relying on low-carbon electricity instead. Demand for electricity is therefore very likely to grow in the future – which makes it critical that its CO2 emissions sharply decrease through the accelerated deployment of low carbon technologies, such as wind and solar power, in the decades ahead.

US power sector CO2 emissions, 1990-2015

For now, US power sector CO2 emissions appear to have turned a corner. While CO2 emissions from the U.S. power sector increased between 1990 and 2005, they peaked shortly thereafter, and then decreased to the point that by 2015, they had fallen by 20% (or 480 million metric tonnes CO2) compared to 2005.

In recently published research, my co-authors and I wanted to understand the drivers behind the drastic fall in the country’s—and individual states’–power sector CO2 emissions, and in particular the role that low carbon technologies such as wind and solar power have already played in reducing US power sector CO2 emissions. Our analysis, published in Environmental Research Letters  used an approach called index decomposition analysis and found that natural gas substituting for coal and petroleum coupled with large increases in renewable energy generation—primarily wind—were responsible for 60% and 30%, respectively, of the decline in CO2 emissions from the US power sector between 2005 and 2015.

Renewable growth in red states

Most of the emissions reductions driven by renewable energy growth came from Texas and states in the Midwest — Iowa, Kansas, Illinois and Oklahoma. While many of these states are not necessarily known for supporting aggressive climate policies, the combination of federal tax credits, state energy policies, decreasing costs of renewables and windy conditions appears to have provided powerful support for renewable energy deployment.

Texas, in particular, is an interesting case. In 2005, it was the leading emitter of U.S. power sector CO2 emissions across the country. But by 2015, its gross reductions from wind energy totaled 27 million metric tons, or more than 5% of the total net US reduction in power sector CO2 emissions since 2005 (i.e., a sixth of the total US reduction attributed to renewables). The state achieved its final renewable portfolio standard (RPS) target in 2008—seven years ahead of its 2015 goal. In addition to reduced costs of turbine technologies, federal tax credits and positive wind conditions also likely played a role in wind’s growth.

Wind generation in Texas, Iowa, Kansas, Illinois and Oklahoma together contributed half of the renewables-related emission reductions (70Mt or 3%-points out of the 20% reduction in US power sector CO2 emissions since 2005).

Over the same period, many states that had relied heavily on coal like Pennsylvania, Georgia, Alabama and Florida, reduced emissions by substituting natural gas for coal in electricity generation. While that prompted a decline in CO2 emissions, it’s important to note that while natural gas emits less CO2 emissions than coal and petroleum when producing electricity it is still a source of CO2 emissions and can only take us so far in decarbonizing the power sector. In addition, methane leakage across the supply chain remains a significant issue–and is not accounted for in this analysis, meaning the overall net greenhouse gas benefit from this natural gas expansion was–potentially significantly—lower.

Need for new policy

While there are positive signs in the power sector—the cost of renewables continues to decline and a growing number of states are taking crucial action to cut CO2 emissions, these trends as well as the specific factors identified in this analysis cannot be relied upon to achieve the deep emissions reductions needed in the decades ahead.

U.S. power sector CO2 emissions are projected to remain relatively flat over the next decade and rise slowly after that, absent new policies. This is particularly significant given that, much of the decarbonization of other sectors such as buildings and transportation will need to rely heavily on electrification.

Ultimately, new policy interventions are necessary, including strong limits on climate pollution – not only in the power sector, but across the entire economy to drive reductions at the pace and scale needed for the US to be 100% clean no later than 2050.

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Getting 100% Clear on 100% Clean

This post, authored by Steve Capanna, Director, U.S. Climate Policy & Analysis, originally appeared on EDF’s Climate-411 blog

Scientists agree that to maximize our chances of averting the worst impacts of climate change, we must stop adding climate pollution to the atmosphere by soon after mid-century. As one of the world’s most advanced economies, the U.S. must reach that goal no later than 2050 – which means transitioning to a 100% clean economy. If this sounds like an ambitious goal, that’s because it is. But it is also what’s needed to protect our economy, our health and our kids’ future.

Why a 100% Clean Economy?

For decades, scientists have warned that catastrophic climate change will result from continued unchecked greenhouse gas emissions. And for decades, our emissions have continued to grow.

Last fall, a Special Report from the Intergovernmental Panel on Climate Change (IPCC), the United Nations body made up of leading scientists from around the world and responsible for assessing the science related to climate change, found that to meet the goals of the Paris Agreement, it will be necessary for the world to achieve net-zero carbon dioxide emissions (adding no more pollution to the atmosphere than we can remove) by soon after midcentury. We also need to achieve deep reductions in other greenhouse gas pollutants like methane. Continued delay will only deepen the challenge, and require us to reduce our emissions even more rapidly.

We’re already seeing the impacts of climate change in communities across the country from record flooding, devastating wildfires, scorching heat waves, and bigger and more damaging storms. Although the impacts are local, climate change is a global problem – which is why the IPCC outlined a global goal. But there are several reasons why the U.S. should strive for achieving a 100% clean economy as soon as possible.

First, the U.S. is the second largest emitter in the world, behind only China. Reaching net-zero emissions globally will only be possible with U.S. leadership. Second, over our history, the U.S. is responsible for by far the most emissions of any other country, more than 85% above China, the second biggest emitter. (Check out this Carbon Brief animation to see the relative emissions contributions of top emitting countries since 1750.) The U.S. has played a major role in creating this problem – we must also play a major role in the solution.

Furthermore, tackling the climate challenge is also just good business. By transitioning as rapidly as we can to 100% clean energy across our economy – including the power sector as well as transportation and industry – we will unleash the power of American innovation to develop cheaper, more efficient clean energy technologies. As global momentum on climate action continues to build, clean energy manufacturing will be an increasingly important industry. Innovative solutions developed by American entrepreneurs can be deployed around the world, helping lower the costs of global emissions reductions while strengthening American industries.

What Exactly Does 100% Clean Mean?

As we substitute zero carbon energy sources like wind and solar for fossil fuels like coal and natural gas, we reduce emissions. We’ve made a lot of progress on this front: according to the National Renewable Energy Laboratory, from 2007-2017, renewable electricity generation more than doubled, and wind and solar generation went from less than 1% of our electricity mix to more than 8%. But we can – and must – do a lot more.

Other sectors of the economy, however, such as air travel, or steel, cement and chemicals manufacturing, are very likely to be difficult and expensive to decarbonize with the technologies we have available or are developing today.

That’s where carbon dioxide removal technologies (CDRs) can play an important role. In comparison to technologies like solar or wind, which generate carbon-free energy, CDRs actually remove carbon dioxide from the atmosphere. As long as we remove as much carbon from the atmosphere as we put into it, we’ll have achieved net-zero emissions – or a 100% clean energy economy.

There are many different types of CDRs, from natural approaches like increasing the amount of forest land and adopting sustainable farming practices, to technologies like direct air capture (DAC) that can suck pollution directly out of the air and store it underground or reuse it in products like fuel, fertilizer, or concrete.

How Do We Do It?

That’s a good question. We know that we are going to need to rapidly shift to cleaner sources of generation in the electricity sector, expand the use of clean electricity in sectors across the economy, advance energy efficiency – and also remove carbon from the atmosphere. The strategies we’ll need to pursue will vary by sector, and given the rapid pace of technology development over the last several years, it’s hard to know which zero-carbon technologies will end up being the most cost-competitive and easy to scale by 2050.

That’s why it’s important that the 100% clean economy goal is focused squarely on environmental results – cutting the pollution that causes climate change without specifying specific technology solutions. This allows for maximum opportunities to deploy a portfolio of technologies and approaches while providing incentives to innovators to find new effective and efficient low-, no-, and negative-emission technologies.

We can achieve this goal, but it will require policies that set declining limits on greenhouse gas emissions; account for the real cost of that pollution; stimulate the research, development and deployment of innovative technologies; and incentivize rapid action, especially in the sectors of the economy that look most challenging to decarbonize.

Climate change is an urgent problem that demands an urgent solution. The time is now to commit to a 100% clean economy that will be cleaner, safer, and more prosperous for all Americans.

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Study: Renewables played crucial role in U.S. CO2 reductions

This blog was co-authored with Jonathan Camuzeaux, Adrian Muller, Marius Schneider and Gernot Wagner.

After a nearly 20-year upward trend, U.S. CO2 emissions from energy took a sharp and unexpected turn downwards in 2007. By 2013, the country’s annual CO2 emissions had decreased by 11% – a decline not witnessed since the 1979 oil crisis.

Experts have generally attributed this decrease to the economic recession, and to a huge surge in cheap natural gas displacing coal in the U.S. energy mix. But those same experts mostly overlooked another key factor: the parallel rise in renewable energy production from sources like wind and solar, which expanded substantially over the same 2007-2013 timeframe.

Between 2007 and 2013, wind generated electricity grew almost five-fold to 168 TWh and utility-scale solar from 0.6 TWh to 8.7 TWh. During the same period, bioenergy production grew 39 percent to 4,800 trillion BTUs.

Given these increases, how much did renewables contribute to the emissions reductions in the United States? In a paper published this month in the journal Energy Policy, we use a method called decomposition analysis to answer just that.

Unpacking the Factors

Decomposition analysis is an established method which enables us to separate different factors of influence on total CO2-emissions and identify the contribution of each to the observed decrease. The factors considered here are total energy demand, the share of gas in the fossil fuel mix (capturing the switch from coal and petroleum to gas), and the share of renewables and nuclear energy in total energy production.

Introducing a new approach for separately quantifying the contributions from renewables, we find that renewables played a crucial role in driving U.S. energy CO­2 emissions down between 2007 and 2013 – something which has previously largely gone unrecognized.

According to our index decomposition analysis, of the total 640 million metric ton (Mt) decrease (11%) during that period two-thirds resulted from changes in the composition of the U.S. energy mix (with the remaining third due to a reduction in primary energy demand). Of that, renewables contributed roughly 200 Mt reductions, about a third of the total drop in energy CO2 emissions. That’s about the same as the contribution of the coal and petroleum-to-gas switch (215 Mt). Conversely, increases in nuclear generation contributed a relatively minor 35 Mt.

While the significant role of renewables in reducing CO2 emissions does not diminish the contribution of the switch to natural gas, it is important to note that the climate benefits of switching from coal and petroleum to gas are undermined by the presence of methane leakage along the natural gas supply chain, the extent of which is likely underestimated in national greenhouse gas (GHG) emissions inventories.

Methane, of course, is a powerful greenhouse gas. Methane leakage from increased natural gas use could have wiped out up to 30% of the short-term GHG benefit (on a CO2-equivalent basis) calculated in this paper of switching from coal and petroleum to natural gas. For the natural gas industry to truly sustain the claim that it has made a positive contribution to reducing the country’s carbon footprint, the methane emissions associated with natural gas must be substantially reduced.

These results show that past incentives to support the expansion of renewable energy have been successful in reducing the country’s emissions, and that decreasing costs for renewable energy offers some hope for continued progress even despite the current administration’s refusal to address climate change.

Such progress, however, will never be sufficient without ambitious climate and clean energy policies- whether at the federal or at the state level – that can drive further emission reductions.

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