Climate change could lead to four times the nitrogen pollution by 2100

 

Climate Change

Climate change could lead to four times the nitrogen pollution by 2100

Livestock was the main contributor to nitrogen emissions, along with synthetic fertilisers, land-use change and manure emissions

Climate change could contribute to pushing nitrogen pollution to 600 tg per year by 2100

Livestock was responsible for about a third of the total nitrogen emissions produced by human activity.iStock

21 Jan 2025, 6:23 pm

Humans currently add around 150 teragrammes (Tg) of reactive nitrogen to the Earth’s land surface each year through agriculture and industry. This amount is more than double the pre-industrial rate, according to a new report.

Climate change could contribute to this rate, raising it to about 600 Tg per year by 2100, which could further increase the levels of nitrogen loss into the environment, the report by the Food and Agriculture Organization of the United Nations, suggested. 

NUE is the ratio of nitrogen recovered in the final output to the total nitrogen used as input. Increasing NUE aims to recover as much of the nitrogen input as possible in the final product, thereby minimising the amount of nitrogen lost in the production process, according to the report released on January 20.

Livestock was the main contributor to nitrogen emissions and was responsible for about a third of the total nitrogen emissions produced by human activity. Synthetic fertilisers, land-use change and manure emissions were the other main causes of nitrogen pollution, the report said. 

Global nitrogen flows have already surpassed the planetary boundaries — a term referring to the environmental limits within which humanity can safely operate, and the degree of this exceedance has dramatically increased since 2015. 

However, the report pointed out that while the exceedance of the global nitrogen planetary boundaries was evident, regional heterogeneity needs to be considered, which requires different formulations of policies and improvement options suitable for each set of local conditions. 

On one hand, the rise in nitrogen fertilisers over the past century has significantly contributed to enhancing agricultural production and bolstering food security and nutrition for an expanding global population. On the other hand, improper use of nitrogen can severely damage air, water and soil quality, result in biodiversity loss and exacerbate climate change.

Global crop yield has been rising steadily from an average of 19 kg of nitrogen per hectare per year in 1961 to 65 kg N/ha/year in 2022. Nitrogen use efficiency, however, declined from 56 per cent in 1961 to 40 per cent in the 1980s and has since increased again to 56 per cent in 2022. 

As per the report, nitrogen pollution was the most severe in North America, Western Europe and certain Asian countries “where fertilisers have been extensively used and misused for decades”. 

NUE ranges varied by country: In Southeast Asia, it decreased significantly from 65 per cent in 1961 to 45 per cent in the 1990s, to increase again to 54 per cent in 2022. In North America, NUE first decreased from 65 per cent in 1961 to below 50 per cent in the 1980s, then increased to 69 per cent in 2022. 

NUE also varied at the crop level. For example, soybeans had an NUE as high as 80 per cent in 2010, while fruits and vegetables had NUEs as low as 14 per cent in the same year. 

The report also offered a series of recommendations. It advised that the fertiliser industry should take urgent action to reduce greenhouse gas emissions during the production of mineral nitrogen fertiliser and encourage the minimisation of wasteful losses during storage, transport and land application.

National governments, authors of the report suggested, should encourage the widespread use of biological nitrogen fixation (a process in which nitrogen gas from the atmosphere is symbiotically fixed into the tissues of certain plants) in locally appropriate crop rotations using leguminous crops, such as soybean or alfalfa.

National governments should create guidelines to assist livestock farmers in adopting the best manure management practices, concentrating on minimising wasteful nitrogen losses to the environment and enhancing its effective use in productive agriculture, the researchers recommended.

Agrifood system policies, they added, should encourage the use of organic nitrogen fertilisers to enhance sustainability. They should also promote spatial planning by redistributing livestock, reducing the number of livestock in areas with high geographical concentration and promoting circular bioeconomy approaches.

The report also advocated that national governments should promote the integration of sustainable nitrogen management in nationally appropriate mitigation actions and nationally determined contributions, including targets to reduce nitrous oxide from agrifood systems to keep in sight the Paris Agreement goal of restricting global warming to 1.5 degrees Celsius above the pre-industrial period.

National governments should alsi set national commitments to reduce nitrogen pollution, including ammonia and nitrates to meet global biodiversity goals, the authors addedd.

Warming climate driving fundamental shifts in Boreal forests: Study

Boreal forests face thinning, rising fire risks and altered carbon storage dynamics

Boreal forests are in a state of disequilibrium, shifting towards a half-open forest regime, the study found.

Himanshu Nitnaware

21 Jan 2025, 6:00 pm

Nearly half of the global boreal forests — spanning Canada, Alaska and Siberia — are undergoing major transitions due to climate change, making them increasingly vulnerable to forest fires and altering their role as a key carbon sink, a new study has revealed. 

These forests are vast and found in the cold, northern regions. However, they are warming four times faster than the global average and are expected to shift into a new ecological regime. This transformation could impact global climate regulation by triggering biome shifts and changes in tree cover dynamics, according to the study published in the journal Proceedings of the National Academy of Sciences (PNAS).

Researchers at Wageningen University and Research analysed tree cover data from 2 million random sample plots, each 6.25 hectares in size, between 2000 and 2020. Their findings highlighted two distinct modes of tree cover in boreal forests: Low-density cover (5-15 per cent) and high-density cover (over 60 per cent). The distribution of these modes varied with mean annual temperatures, reflecting a climate-sensitive pattern.

After millenia as a carbon sink, over a third of Arctic Boreal region turns into carbon emitter

Boreal forests are in a state of disequilibrium, shifting towards a half-open forest regime, the study found.

“The low-density mode occurred throughout the temperature gradient but was most dominant in the cold boreal. High-density forests were only present in the warmer half of the boreal biome,” the study stated. 

The authors stated that both types of tree cover were found along different parts of the temperature range, indicating the possibility of alternative states.

Over the two decades analysed, warmer southern boreal forests, characterised by dense tree cover, showed a decline, while colder northern forests with sparse cover exhibited increased density. 

The scientists concluded that the balance between total tree cover losses and gains would stabilise by 2100. Future forests are expected to settle at intermediate tree cover levels of 40-45 per cent in warmer regions and 25-30 per cent in colder, lower boreal areas.

Experts urge a new global pact at COP16 to safeguard boreal and temperate forests

Boreal forests are in a state of disequilibrium, shifting towards a half-open forest regime, the study found.

“Based on the tendencies of change in the period 2000-2020, the boreal forest will move toward an open state with a tree cover between 30 and 50 per cent, decreasing gradually from the south to the north,” the study said, backed by the simulations. 

It suggested that the boreal biome shifting to an open state indicates that its current distribution is unstable and temporary. 

The shift towards open forests is attributed to warming exceeding temperature thresholds, particularly in dense southern boreal forests. This leads to reduced growth rates in tree species, increased mortality and greater vulnerability to threats like timber logging, insect outbreaks and wildfires.

The study projects that the warmer, denser forests may thin by 20 per cent, while sparse forests in colder regions could become 40 per cent denser. These transitions are expected to alter the biome’s carbon storage capacity and increase fire risks. The findings are, however, conservative projections and do not fully account for all future effects of climate change on the said tree cover changes.

‘Restoring tree cover may lead to global warming but only in some places’

Boreal forests are in a state of disequilibrium, shifting towards a half-open forest regime, the study found.

The paper stated, “Especially dry forests (for example, those north of the Great Plains in North America or in inner Asia) may be lost entirely to alternative vegetation types, such as steppe grasslands or shrublands, under continued warming.”

The shift to an open forest state could increase biomass carbon uptake by 17.7 gigatonnes by 2100, an 11.4 per cent rise compared to current levels. However, the study cautioned that this gain could be outweighed by several factors.

“First, the net increase of aboveground carbon will eventually level off with tree density and when forests reach their northern terrestrial limits at the Arctic Ocean. Second, future forests may be shorter in height and thus store less biomass for any given tree cover density,” the study said.

Finally, permafrost thawing, which facilitates forest expansion in colder regions, may release significant amounts of stored soil carbon, potentially negating carbon uptake

Study identifies 20 regions in Arctic most vulnerable to climate change, permafrost common denominator

Boreal forests are in a state of disequilibrium, shifting towards a half-open forest regime, the study found.

The study also warned that transitioning to open forests increases the risk of wildfires. Low- and high-density forests currently resist burning due to a lack of fuel or microclimatic conditions. However, open forests, with their sparse yet flammable vegetation, are likely to experience novel and severe fires.

“It is therefore likely that large parts of a future open forest will experience novel fire regimes. Some of these forests, especially in the southern or drier range of the biome, may not be able to recover from severe fires, resulting in forest loss,” the study noted.

The study concluded that boreal forests are in a state of disequilibrium, shifting towards a half-open forest regime. This could reduce the biome’s ability to regulate global climate and store carbon, while also complicating predictions of future fire behaviour and ecosystem dynamics, it warned.