Two reports released this week about global energy sector carbon
emissions and atmospheric CO2 concentration may be confusing. At least, they were
to me initially.
On Wednesday the International Energy Agency reported that carbon emissions from the global
energy sector remained roughly flat for the second year in a row. According to
IEA, 2014 emissions were 32.3 billion metric tons and 2015 emissions were 32.1
billion metric tons. In fact, then, emissions from the global energy sector
decreased slightly year-over-year. Those same years, global GDP increased 3.4%
and 3.1%, respectively. (See, e.g., Chris Mooney’s March 16 Washington Post piece). This is significant because it
indicates that since 2013 the global economy grew while economy-related carbon emissions did
not. It is welcome news, obviously, confirming that we are seeing a decoupling
of greenhouse gas emissions from economic activity. Put another way, energy
intensity – the quantity of energy required to produce a unit of economic
output – is decreasing. We're getting more efficient – Yay! – as we must if we are to succeed in mitigating global warming's worst-case outcomes caused by GHG emissions from human activities,
such as combusting fossil fuels to power
our lives.
Also this week the U.S. National Oceanic and Atmospheric
Administration (NOAA) reported that the
atmospheric concentration of CO2 increased by 3.05 parts per million in 2015,
the largest year-over-year spike observed in the 56 years NOAA has been
measuring atmospheric CO2 concentration at its Mauna Loa Observatory in Hawaii.
How can carbon emissions from the global energy sector be
flattening or slightly declining while the observed concentration of
atmospheric CO2 is spiking? As these reports had appeared in my Facebook
newsfeed in posts by Penn State climate scientist Dr. Michael Mann and
Washington Post Energy and Environment writer Chris Mooney, I reached out to
them via Twitter seeking clarification. Professor Mann responded, “Emissions
& concentrations don't track on annual basis. The latter is a lagging
indicator.” Chris Mooney responded, “One thing to note is that IEA is only
energy related emissions. El Nino also created fires, droughts.” Science
blogger Greg Laden also replied, pointing out that drying tropical forests grow
less, take up less CO2, and are more susceptible to fire.
Confusion resolved. Energy sector emissions may have stalled,
but the lag between emissions and observed atmospheric CO2 concentration, along with other factors like El
Nino, drying rain forests and drought, and other sources of emissions like the
massive Indonesian
forest fires mean that 2015 still saw a record spike in atmospheric CO2
concentration.
As Professor Mann’s reply highlights, it takes time for CO2 emitted
as a result of human activities to mix in the atmosphere. The CO2 concentration
increases we measure for a given year reflect emissions and other contributing factors
from years past. As he notes, concentration lags emissions. On the matter of
lags, I would add that because of inertial lags in the climate system it takes
decades – about 40 years –for GHGs emitted
in a given year to affect global average surface temperature.(*) The scary
implication of the 40-year lag is that the global average surface temperatures we
are experiencing now – almost 1°C above the mid-20th century average – are the
product of emissions accumulated up through … the 1970s. And we’ve emitted tens
of billions of tons of CO2 and other GHGs over the decades since.
CO2 emissions have increased by more than 90% since 1970 according to the
Environmental Protection Agency. The temperatures that will prevail around the
globe 40 years from now will reflect the CO2 and other GHGs we emit today (and
what has accumulated up through today). That is both cause for worry and reason
to act aggressively … now! … to bring down carbon emissions.
Which brings me to this important take-away. The
significance of the IEA data cannot be overstated. The fact that global economic
production grew while carbon emissions simultaneously declined proves that taking
action to mitigate global warming by switching from fossil fuel-based energy
generation to renewable sources and energy efficiency does not correspond to a
decline in economic growth. These recent IEA data together with a growing body
of evidence show the opposite, in fact. In recent years, numerous independent
analyses focused at levels of geographic scope from municipalities to states to nations to global
have found that moving to cleaner, renewable energy sources, improving energy efficiency,
and sustainably managing natural resources produce economic benefits that 1) are
greater than business-as-usual, do-nothing scenarios and 2) exceed their costs.
Often, the analyses reach this conclusion even without factoring in adverse climate
impacts avoided and public health benefits gained. Not that their arguments
were ever strong, but those who object to climate action on economic grounds
can no longer do so credibly. Certainly, given the ample evidence available,
their tired old shibboleths should not be allowed to go unrebutted. Rather, in fact,
advocates need to marshal the evidence – economic, public health, ecological, security, etc. – and forcefully, articulately make the case for concerted climate
action now.
