Seabird Guano Both Warms the Earth and Cools It
The world’s seabirds don’t just live off the land, they also nourish it: their excrement delivers 591,000 tons of nitrogen and 99,000 tons of phosphorus to feed plant communities in the soil and the water.
One polar plant community that happens to be flourishing is now to be found on the surface of Greenland’s icecap: green things are growing so well they are darkening the surface, which then reflects less light and absorbs more warmth. This algal darkening could be responsible for at least 5%, and possibly 10%, of the island’s total ice melt each summer.
And although the Arctic tundra wetlands are known to deliver between 16 and 27 million tons of methane to the atmosphere every year, they have unexpected competition in the natural greenhouse gas emission stakes.
New research reveals that the Amazon floodplain’s rainforest itself – most frequently thought of as a carbon sink for the planet – releases up to 21 million tons of methane to the atmosphere each year. This is more methane from one forest than from all the world’s oceans.
This catalogue of unexpected information has been made available by geographers, climate scientists and biologists involved in global warming research: each finding is confirmation that the planet must be considered as an intricate economic system, involving a continuous traffic between plants, animals, oceans, icecaps, atmosphere and the rocky surfaces of the continents. It also confirms that the accounting of these exchanges is still incomplete.
The irony is that in the process of trying to understand the climate change that poses a potential threat to human civilisations, humans now know their planet better than ever before.
But each individual bit of research confirms that there is still some way to go before the picture is complete. US scientists two years ago confirmed that ammonia from the guano left behind by breeding seabirds in the Arctic played a role in cloud droplet formation, which in turn reflected sunlight to keep the Arctic cool.
But Spanish and Mexican scientists wanted to know more. They report in Nature Communications that the 320 species of the world’s seabirds probably add up to 1,045 million individual birds, including 804 million breeding birds and their chicks.
Seabirds – gulls, penguins, puffins, guillemots, auks, albatrosses, shearwaters, fulmars, cormorants and so on – tend to nest in colonies, leaving over many millennia deposits of guano so rich and thick that in the 19th century nations fought over this agricultural resource.
Ten species, they found, contributed more than 60% of the nitrogen and phosphorus, two elements essential to all life. These contributors might not be the most numerous: the five penguin species and four albatrosses – big birds that spent long periods in their colonies – were the biggest contributors per individual.
The nitrogen gets from the colonies to coastal waters to increase primary plant life. So what the study’s authors daintily call “ornitheutrophication” has, they say, “geochemical and environmental relevance on a global scale.”
European and US scientists who looked at the mysterious darkening of the Greenland snows each summer were concerned with environmental relevance: Greenland is host to so much ice that, were it all to melt, sea levels would rise by seven metres, to drown most of the world’s coastal cities.
They used instruments every day over a 56-day period to confirm that the ice sheet reflected significantly less light as the algae grew. They also concluded that algal growth was responsible for 70% of the variance in the ice sheet’s albedo (the climate scientist’s term for the capacity of land, ice or water to reflect solar radiation).
“As the climate warms, the area that the algae can grow in will expand, so they’ll colonise more of the ice sheet,” said Marek Stibal, an ecologist at Charles University in Prague, who led the research.
“Additionally, the growing season will lengthen, so the contribution of algae to melting of the ice will probably increase over time.”
British, Brazilian, Canadian and US scientists report in the journal Nature that they monitored methane flow from the stems of 2,357 individual trees at 13 locations on the Amazon floodplain.
Methane – sometimes called marsh gas – is a natural greenhouse gas linked to decomposing vegetation, and is around 34 times more powerful than carbon dioxide at trapping atmospheric heat.
Mosaic of Measurement
The scientists found that methane release from the Amazon trees was 200 times that from temperate wet forests and tropical peat swamp woodlands.
This finding, like the evidence from sea bird nutrients and glacial algae, represented yet another piece in the mosaic of meticulous measurements that provide the basis for a better understanding of how climate works.
“We are not, in any way, saying that trees are bad for the environment – this is how natural forests function. We now have a fuller picture of the sources of greenhouse gas emissions and this could help to inform how environmental change can have a knock-on effect on the tropical wetland methane source,” said Sunitha Pangala, then at the Open University but now at the University of Lancaster in the UK, who carried out the study.
“Emissions from these Amazon trees are still only half as much as those created by humans in the form of landfill and waste, so we should be targeting reductions in human emissions.”