Guest blog by James Curran (LINK Honorary Fellow) and Sam Curran
When I retired from paid work, I was eager to dive back into science. For years, I had an idea brewing that – if my hypothesis was right – would have important consequences for the planet, but I never had the time to explore it. Teaming up with my son Sam, we embarked on this journey, convinced that our simple idea must have already been investigated. Surprisingly, it hadn’t.
As independent scientists, we relied on publicly available data for our investigation. Fortunately, when it comes to carbon dioxide (CO2) levels in the atmosphere, there’s a wealth of open-access data. The longest record comes from the Mauna Loa Observatory, perched on top of a volcano in Hawaii, in the middle of the Pacific Ocean and fairly close to the Equator. This high-quality data record started in 1957 and continues to this day.
When plotted over time, these data form the well-known Keeling Curve. The saw-tooth pattern of the curve (Figure 1) is particularly intriguing. It occurs because most of the Earth’s land mass is in the Northern Hemisphere and, during the northern summer, the abundant vegetation of the North absorbs a huge amount of CO2 from the atmosphere.
In the northern winter, some of this CO2 is released back into the atmosphere through natural biodegradation of dead vegetation, but a portion remains locked in roots, soil, and dormant woody matter. The portion of CO2 drawn out by vegetation and locked away is known as natural sequestration. The overall curve of CO2 concentrations rises year-on-year, of course, due to the additional anthropogenic CO2 emissions that we pump out continuously.
For our research, we focused on the curve’s saw-tooth pattern because it is a direct reflection of the overall health of the Earth’s biosphere and, particularly, its ability to provide some balance against CO2 emissions.
It is worth noting here a widely held belief that sequestration is increasing globally due to a) warming temperatures that encourage vegetation growth, especially in sub-Arctic regions, and b) higher atmospheric CO2 acting as a fertiliser of plant growth. However, it’s also acknowledged that sequestration will likely decline at some point in the future due to heat stress, wildfires, drought, storms, floods, and the spread of new pests and diseases. Enhanced seasonal permafrost melt may also release additional CO2 into the atmosphere.
In 2016, we published a couple of short peer-reviewed articles relating to this topic. Now, almost ten years later, it seemed like a good time to validate our earlier, tentative findings. Our third paper, recently published, reinforces the earlier and alarming finding that natural sequestration peaked in 2008 (the earlier work suggested 2006) and is now declining. It had been increasing at 0.8% per year in the 1960s but is now declining at 0.25% per year. To put this in perspective, sequestration would have increased by half in 50 years, whereas it would now decline by half in about 250 years. Does this matter? Absolutely.
Currently, atmospheric CO2 increases by about 2.5 parts per million (ppm) each year. If the biosphere’s sequestration ability had continued growing as it did in the 1960s, the annual increase would now be smaller at +1.9 ppm per year. That’s a big difference.
Right now, just to make up for declining sequestration, anthropogenic emissions would need to fall by 0.3% per year. This is substantial, considering emissions have been increasing at roughly +1.2% per year.
These damaging effects will only get worse as the decline of sequestration is accelerating.
Everyone reading this blog will well understand the implications. The climate and nature emergencies are locked together.
It’s urgent that every effort is made to rebuild biodiversity and associated ecosystem services, including sequestration. Deforestation must stop. Nature restoration must be encouraged. Forest fires must be prevented. For large-scale habitats, which are more resilient and offer enhanced ecosystem services, defragmentation must be prioritized. Soil must be nurtured. Timber and fibre products must be reused for as long as possible, as part of a wider circular economy.
All this in addition to an end to burning of fossil fuels – of course.
The hypothesis we held for many years, as feared, has proven correct. Retirement may be upon me, but for my son, my granddaughter – for all our loved ones and for future generations, the need for action grows ever greater, ever more radical, and ever more urgent.
For further reading, see the short research article.
Photo by Roxanne Desgagnés on Unsplash