The Secretary of Environmental Affairs would be required to adopt a “2050 statewide greenhouse gas emissions limit of not more than net-zero emissions” under legislation that the Senate passed yesterday. Both the House speaker and the Governor have also spoken favorably of the “net-zero” goal, so the requirement is likely to become law.
Why “net-zero”? Is it enough? There is a difference between “zero” and “net-zero.” Zero would imply that we never used fossil fuels for any purpose. That does not seem a realistic goal to set for 2050. While electricity can substitute for fossil fuel power in most contexts, it seems likely that we may need to continue to use fossil fuel for backup power for critical functions like hospitals and emergency vehicles.
“Net-zero” allows the Commonwealth to do a balanced accounting for carbon emissions, including things like forests that take carbon dioxide out of the atmosphere to offset our continuing limited fossil fuel use. If the whole world could achieve “net-zero” then at least we would have stopped increasing the amount of carbon dioxide in the atmosphere. The International Panel on Climate Change has recommended this net-zero goal. They find that net zero by 2050 is likely necessary if we are to hold warming to 1.5 degrees centigrade.
In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO2 emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range).1IPCC, Global warming of 1.5 Degrees Centigrade, Chapter Two Executive Summary
There are two ways to account for atmospheric carbon dioxide. First, for state or national goal setting, we tend to focus on the tons of carbon dioxide that we are putting out annually. So, we think in terms of annual reduction targets and long-term stretch goals for annual emissions like “net-zero” by 2050.
Second, since carbon dioxide remains in the atmosphere for thousands of years, we need to look at the cumulative amount that has been released and now remains in the global atmosphere, expressed as parts per million. The parts-per-million goal feeds in to the models that compute how much heat is trapped by the “greenhouse” effect. The models work from the parts-per-million number and other factors to determine how much temperatures are likely to rise overall.
Because the parts-per-million level is cumulative of all the annual emissions, it matters a lot how fast we get to “net-zero.” The faster we get there, the less total emissions and the lower the parts-per-million level. If world emissions remain high for several more decades then we will experience a lot of irreversible warming, even if we ultimately get to “net-zero.”
So far the world hasn’t made much progress in reducing annual emissions, much less the total stock of carbon dioxide in the atmosphere. For all of our effort and conversation, it appears that 2019 was the highest emission year ever. Fundamentally, economic growth requires more energy use and the increase in energy use is outpacing our rate of conversion from fossil energy to other sources of energy.
China accounts for a large share of both global economic growth and the growth in carbon dioxide emissions. Other developing countries are also expanding emissions. We certainly cannot begrudge these countries their economic growth — they are entitled to enjoy the mobility and prosperity that we enjoy.
Given that the world is likely to fail to reduce emissions for some years, we will eventually need to achieve negative emissions and reverse the accumulation of carbon dioxide if we hope to limit global temperature rise. Most of the modeled scenarios in which we are able to limit warming depend on as yet unknown methods for pulling carbon dioxide out of the atmosphere.
All analysed pathways limiting warming to 1.5°C with no or limited overshoot use [carbon dioxide removal] to some extent to neutralize emissions from sources for which no mitigation measures have been identified and, in most cases, also to achieve net negative emissions to return global warming to 1.5°C following a peak (high confidence). The longer the delay in reducing CO2 emissions towards zero, the larger the likelihood of exceeding 1.5°C, and the heavier the implied reliance on net negative emissions after mid-century to return warming to 1.5°C (high confidence).IPCC, Global warming of 1.5 Degrees Centigrade, Chapter Two
We should see the “net-zero” goal for Massachusetts in this larger context. “Net-zero” is not an endpoint. It is a waypoint on a path to a further goal of “net negative.” Targeting “net-zero” by 2050 will not deliver us from the risk of climate change. But by pushing hard for our economy to be greener, we are supporting innovation in energy production, energy storage and energy conservation.
Supporting energy innovation is probably critical to our future. Wholesale reductions in emissions have so far proven difficult for every nation, involving sacrifices that people are unwilling to make. The most significant reductions have come because natural gas has become a cheaper fuel source than coal. Both coal and natural gas generate carbon dioxide, but coal generates more. (See for example, Massachusetts.) Our hope has to be that through continued innovation clean technology will become so cheap, reliable, and convenient that people want to switch to it voluntarily.
So, I’m glad that we are considering a more ambitious “net-zero” goal for the transformation of the Massachusetts economy and I am hopeful that in this legislative session we will enact the new goal and fully support it with strong monitoring and enforcement as contemplated in the Senate legislation.
For details on what else is in the package, please see this post.