Showing posts with label altitude. Show all posts
Showing posts with label altitude. Show all posts

Saturday, April 12, 2014

Methane buildup in the atmosphere

Levels of carbon dioxide (CO2) in the atmosphere are now firmly above the 400 parts per million (ppm) level, as illustrated by the graph below, from
As above graph shows, levels of CO2 go up and down with the seasons. Even higher levels are expected to be reached in May 2014. Importantly, 400 ppm is 143% its pre-industrial peak levels of 280 ppm.

Levels of methane (CH4) in the atmosphere are rising even faster. According to IPCC AR5, methane levels were 1798 ppb in 2010 and 1803 ppb for 2011. A graph included in an earlier post shows historic levels of CH4, CO2 and N2O levels, highlighting methane's steep rise (now some 250% its pre-industrial level). The graph below, based on a plot by NOAA, shows the rise of methane over the past few decades and also shows that methane levels similarly go up and down with the seasons.

Globally, IPCC/NOAA figures suggest that abundance of methane in the atmosphere did reach 1814 ppb in 2013 and is rising with some 5 to 6 ppb annually. IASI data show that - at the hight of the northern summer, in August 2013 - mean methane levels rose strongly, to levels well above 1800 ppb, as also discussed in posts such as this one.

Next to seasonal variations, methane levels also differ depending on altitude. Often, when mean methane values are given, readings at 14,383 feet altitude are used, as methane typically reaches its highest levels at this altitude.

The image on the right compares methane levels for 2013 and 2014 at this altitude over six recent days, with a.m readings and p.m. readings for each day.

Around this time of year in 2013, as the graph shows, methane levels went through the 1800 ppb mark. The same thing occurred this year, while levels have meanwhile increased with a few ppb, so at first glance methane's rise appears to continue as anticipated by the IPCC.

While the above is very worrying, the situation may be even more dire than this. The graph below compares methane levels in 2013 and in 2014, averaged over the same six-day period (April 5 through to April 10) and at six different altitudes.

Above image indicates that, while the difference between 2013 and 2014 at lower altitudes (8,367 feet and 14,383 feet) may seem relatively small, increases at higher altitudes may be much stronger. In other words, rather than rising in a similar way across all altitudes, methane may in fact be building up much more strongly at higher altitudes.

This frightening possibility was raised a few times at this blog, such as in the altitude analysis in January 2014 and in the post Quantifying Arctic Methane, which noted that IPCC-estimates of global methane levels may rely too much on low-altitude data collected over the past few decades. Indeed, the total methane burden may already be rising much more rapidly than the IPCC is anticipating, also because methane is rising in the atmosphere, increasing the burden especially at higher altitudes, as evidenced by increasing occurence of noctilucent clouds.

The above analysis uses a limited dataset, just like the previous one, but if verified by further analysis, it could be that a dramatic rise in the presence of methane in the atmosphere is occuring without showing up at lower altitudes. This could also explain how earlier releases of methane from hydrates could have been ignored by many, i.e. relatively small increases in methane levels at relatively low altitudes may have given a false reassurance that such releases were not adding much methane to the atmosphere. Further analysis, comparing satellite data at different altitudes over the years, could give more clarity on these points.

Saturday, January 25, 2014

Higher Altitude Methane Rise

Dramatic methane releases from the Arctic Ocean seafloor have been documented at this blog over the past few months. While the most recent IPCC figures for emissions from hydrates and permafrost are only 7 Tg per year, a recent post estimates current emissions from hydrates at 99 Tg per year, a figure that is growing rapidly. Furthermore, as discussed in an earlier post, the IPCC's estimated annual increase in global methane levels may seem small, but this figure appears to be based on low-altitude data collected over the past few decades.

These high methane releases undoubtedly contribute to higher global levels, but they may not (as yet) translate into higher global averages due to the way data are collected and figures are averaged and calculated. 

Global levels can be calculated by adding up and averaging readings from all measuring stations around the world. This works well for conventional emissions such as from wetlands, from agriculture or from burning fuel. Such emissions originate from numerous land-based sources that are spread out over large areas, while each emitting relatively small quantities of methane periodically or continuously, which makes it easy for hydroxyl to brake down this type of methane before it rises up into the air. Thus, such emissions can be relatively easily measured from land-based measuring stations. 

By contrast, the Arctic Ocean covers only 2.8% of the Earth's surface and releases from hydrates originate in only parts of the Arctic Ocean. Thus, the methane that enters the atmosphere over the Arctic Ocean is very concentrated to start with. Furthermore, hydroxyl levels in the Arctic atmosphere are low, especially at this time of year. As a result, much of the methane that enters the atmosphere over the Arctic Ocean will rise higher up into the atmosphere without being broken down, and much of the methane will continue to be present over the Arctic for years, exercizing methane's very high initial warming potential. 

There are only a few measuring stations in the Arctic and they are all land-based, making that measurements can be taken at altitudes that are too low to capture the full scale of the methane concentrations that have formed as a result of methane releases from the Arctic Ocean seafloor over the past few months. The local nature and further characteristics of releases from the Arctic Ocean can make that they are underestimated or even ignored in measurements taken at land-based stations and in global levels that are calculated from such data. 

The situation can be tested by looking at peak levels of methane showing up at specific altitudes, as measured by satellite sensors, specifically at two altitudes, i.e. at 14,385 Ft (or 4,385 m) and at 19,820 Ft (or 6,041 m), since methane as measured by the IASI MetOp polar-orbiting satellite shows up most prominently at these altitudes over the Arctic. Thus, to detect methane originating from hydrates under the Arctic Ocean, it's best to look at peak levels at these altitudes. The image below shows IASI data available in January 2013 and in January 2014, for these two altitudes.  

The results of this analysis are quite disturbing, for two reasons. Firstly, January 2014 peak levels have increased strongly, compared to January 2013 peak levels. Secondly, the rise in average peak readings has been most dramatic at the higher altitude (from 2066 ppb in 2013 to 2240 ppb in 2014). 

This suggests that huge quantities of methane have indeed been released from hydrates under the Arctic ocean, and that much of the methane is rising and building up at higher altitudes. The increasing appearance of noctilucent clouds further confirms indications that methane concentrations are rising at higher altitudes. 

Of course, the above analysis uses a limited dataset, but if verified by further analysis, it would confirm a dramatic rise in the presence of methane in the atmosphere due to releases from hydrates. Moreover, it would confirm the immensity of threat that releases from the Arctic Ocean will escalate and trigger runaway warming. The risk that this will eventuate is unacceptable, which calls for comprehensive and effective action such as discussed at the ClimatePlan blog