During August 2013, the Scripps Institution of Oceanography measured an average of 395.15 ppm CO2 concentration at their Mauna Loa, Hawai’i Observatory.
This value is important because 395.15 ppm is the largest CO2 concentration value for any August in recorded history. This year’s July value is 2.74 ppm higher than August 2012′s! Month-to-month differences typically range between 1 and 2 ppm. This particular year-to-year jump is clearly well outside of that range. This change is in line with other months this year: February’s year-over-year change was +3.37 ppm and May’s change was +3.02 ppm. Of course, the unending trend toward higher concentrations with time, no matter the month or specific year-over-year value, as seen in the graphs below, is more significant.
The yearly maximum monthly value normally occurs during May. This year was no different: the 399.89ppm mean concentration in May 2013 was the highest value reported this year and, prior to the last six months, in recorded history (neglecting proxy data). I expected May of this year to produce another all-time record value and it clearly did that. May 2013′s value will hold onto first place all-time until February 2014, due to the annual CO2 oscillation that Figure 2 displays.
Figure 1 – Time series of CO2 concentrations measured at Scripp’s Mauna Loa Observatory in August from 1958 through 2013.
CO2Now.org added the `350s` and `400s` to the past few month’s graphics. I suppose they’re meant to imply concentrations shattered 350 ppm back in the 1980s and are pushing up against 400 ppm now in the 2010s. I’m not sure that they add much value to this graph, but perhaps they make an impact on most people’s perception of milestones within the trend.
How do concentration measurements change in calendar years? The following two graphs demonstrate this.
Figure 2 – Monthly CO2 concentration values (red) from 2009 through 2013 (NOAA). Monthly CO2 concentration values with seasonal cycle removed (black). Note the yearly minimum observation occurred ten months ago and the yearly maximum value occurred three months ago. CO2 concentrations will decrease through October 2013, as they do every year after May, before rebounding towards next year’s maximum value. The red points and line demonstrate the annual CO2 oscillation that exists on top of the year-over-year increase, which the black dots and line represents.
This graph doesn’t look that threatening. What’s the big deal about CO2 concentrations rising a couple of parts per million per year anyway? The problem is the long-term rise in those concentrations and the increased heating they impart on our climate system. Let’s take a longer view – say 50 years:
Figure 3 – 50 year time series of CO2 concentrations at Mauna Loa Observatory (NOAA). The red curve represents the seasonal cycle based on monthly average values. The black curve represents the data with the seasonal cycle removed to show the long-term trend (as in Figure 2). This graph shows the relatively recent and ongoing increase in CO2 concentrations.
As a greenhouse gas, CO2 increases the radiative forcing of the Earth, which increases the amount of energy in our climate system as heat. This excess and increasing heat has to go somewhere or do something within the climate system because the Earth can only emit so much longwave radiation every year. Additional figures below show where most of the heat has gone.
CO2 concentrations are increasing at an increasing rate – not a good trend with respect to minimizing future warming. Natural systems are not equipped to remove CO2 emissions quickly from the atmosphere. Indeed, natural systems will take tens of thousands of years to remove the CO2 we emitted in the course of a couple short centuries. Human technologies do not yet exist that remove CO2 from any medium (air or water). They are not likely to exist for some time. Therefore, the general CO2 concentration rise in Figures 2 and 3 will continue for many years.
This month, I will once again present some graphs that provide additional context for CO2 concentration. Here is a 10,000 year view of CO2 concentrations from ice cores to compare to the recent Mauna Loa observations:
Figure 4 – Historical CO2 concentrations from ice core proxies (blue and green curves) and direct observations made at Mauna Loa, Hawai’i (red curve).
Clearly, concentrations are significantly higher today than they were for thousands of years in the past. While never completely static, the climate system our species evolved in was relatively stable in this time period.
Or we could take a really, really long view:
Figure 5 – Historical record of CO2 concentrations from ice core proxy data, 2008 observed CO2 concentration value, and 2 potential future concentration values resulting from lower and higher emissions scenarios used in the IPCC’s AR4.
Note that this graph includes values from the past 800,000 years, 2008 observed values (10ppm less than this year’s average value will be) as well as the projected concentrations for 2100 derived from a lower emissions and higher emissions scenarios used by the 2007 IPCC Fourth Assessment report. If our current emissions rate continues unabated, it looks like a tripling of average pre-industrial (prior to 1850) concentrations will be our future reality: 278 * 3 = 834. This graph also clearly demonstrates how anomalous today’s CO2 concentration values are in the context of paleoclimate. It further shows how significant projected emission pathways could be when we compare them to the past 800,000 years. It is important to realize that we are currently on the higher emissions pathway (towards 800+ppm; yellow dot).
The rise in CO2 concentrations will slow down, stop, and reverse when we decide it will. It depends primarily on the rate at which we emit CO2 into the atmosphere. We can choose 400 ppm or 450 ppm or almost any other target (realistically, 350 ppm seems out of reach within the next couple hundred years). That choice is dependent on the type of policies we decide to implement. It is our current policy to burn fossil fuels because we think doing so is cheap, although current practices are massively inefficient and done without proper market signals. We will widely deploy clean sources of energy when they are cheap; we control that timing. We will remove CO2 from the atmosphere if we have cheap and effective technologies and mechanisms to do so, which we also control to some degree. These future trends depend on today’s innovation and investment in research, development, and deployment. Today’s carbon markets are not the correct mechanism, as they are aptly demonstrating. But the bottom line remains: We will limit future warming and climate effects when we choose to do so.
I mentioned above that CO2 is a greenhouse gas. If CO2 concentrations were very low, the average temperature of the planet would be 50°F cooler. Ice would cover much more of the planet’s surface than it does today. So some CO2 is a good thing. The problem with additional CO2 in the atmosphere is that it throws off the radiative balance of the past 10,000 years. This sets in motion a set of consequences, most of which we cannot anticipate simply because our species has never experienced them. The excess heat absorbed by the climate system went to the most efficient heat sink on our planet, the oceans:
Figure 6 – Heat content anomaly from 1950 to 2004 from Murphy et al., 2009 (subs. req’d).
20th century global surface temperature rise measured +0.8°F. That relatively small increase, which is already causing widespread effects today, is a result of the tiny heat content anomaly shown in red in Figure 6. This situation continued since Murphy’s 2009 publication.
Figure 7 – Oceanic heat content by depth since 19
This figure shows where most of the excess heat went since 2000: the deep ocean (>700m depth). The heat content change of the upper 300m increased by 5 * 10^22 Joules/year in that time (and most of that in the 2000-2003 time span) while the 300-700m layer’s heat increased by an additional 5 * 10^22 J/y and the >700m ocean’s heat increased by a further 8 * 10^22 J/y. That’s a lot of energy. How much energy is it? In 2008 alone, the oceans absorbed as much energy as 6.6 trillion Americans used in the same year. Since there is only 7 billion people on the planet, the magnitude of this energy surplus is staggering.
More to the point, deep water heat content continued to surge with time while heat content stabilized in the ocean’s top layers. Surface temperature measurements largely reflect the top layer of the ocean. If heat content doesn’t change with time in those layers, neither will sea surface temperatures. The heat is instead going where we cannot easily measure it. Does that mean “global warming has stopped” as some skeptics recently claimed? No, it means the climate system is transferring the heat where and when it can. If the deep ocean can more easily absorb the heat than other media, then the heat will go there.
The deep ocean will not permanently store this heat however. The globe’s oceans turn over on long time scales. The absorbed heat will come back to the surface where it can transfer to the atmosphere, at which point we will be able to easily detect it again. So at some point in the future, perhaps decades or a century from now, a temperature surge could occur. We have been afforded time that many scientists did not think we had to mitigate and adapt to the changing climate. That time is not limitless.