Arctic News: Emissions and Temperature Rise

The image below shows the Planet by land biome, i.e. forests, grassland, desert, tundra and shrubland. Rainforests are common in equatorial areas and they have steady temperatures year-round and high precipitation allowing for evergreen and semi-evergreen trees. Boreal forests, also called Taiga, cover much of the planet’s northern latitudes and their trees are coniferous (non-shedding), while trees in temperate areas do shed their leaves (deciduous).

Forests come with many climate benefits. Trees take carbon out of the atmosphere and store the carbon in the trees and in the soil, thus reducing global warming. Less carbon dioxide in the atmosphere also reduces ocean acidification. The top layer (canopy) of rainforests contains giant trees that can grow to heights of 75 m (about 250 ft) or more. The canopy prevents much sunlight from reaching the ground, thus cooling the surface locally. Trees hold the soil together and can pump up water from deep in the soil and, through evaporation, keep the surface and soil cool, thus also avoiding erosion and reducing fire hazards.

So, trees are responsible for cooling in many ways. Trees can darken the surface, which can cause more sunlight to be absorbed, thus resulting in more warming, but trees can also cause cooling in another way. Trees also release terpines and other biogenic volatile organic compounds (BVOCs) into the air. These BVOCs can react chemically in the atmosphere to form aerosols that reflect incoming solar radiation and thereby cause global cooling. These aerosols can also act to start clouds to form that result in rainfall and that shade the surface, reflecting more solar radiation back into space and thus cause further global cooling.

While BVOCs have many benefits, they can also indirectly increase potent greenhouse gases including ozone and methane by depleting hydroxyl. A study led by Gillian Thornhill found that this could cause half the cooling effects of BVOCs to be lost. A recent study led by James Weber found that, when all the effects are combined, they can reduce the net climate benefit of wide scale tree-planting by up to one third.

The above image shows that organic matter aerosol optical thickness (55 nm) as high as 0.93 τ was recorded over North Australia on October 14, 2025 06:00 UTC.

Anyway, the overall net climate benefit of trees is huge and is underestimated. While trees can cause some warming, they also cause more cooling. Their BVOCs are responsible for some depletion of hydroxyl, but this should be no reason to stop supporting forests. Instead, climate action should strongly support forests and greater hydroxyl abundance is better accomplished by cleaning up industry sectors such as agriculture, transport and electricity generation.

IPCC downplays the temperature rise

The IPCC downplays the temperature rise in efforts to hide some of the most effective and necessary action, e.g. by presenting the impact of land use, gases and aerosols in most peculiar ways. Instead of comparing the climate impact of forests versus agriculture in commonly comprehensible language, such as a rise in degrees Celsius, the IPCC uses technical terms to make things less comprehensible for the typical reader (and voter).

As an example, the IPCC seeks to present deforestation as a change in land use that results in greater cooling, e.g. by arguing that deserts reflect more light back into space. As another example, the IPCC makes it look as if the temperature started rising only from 1850-1900, in efforts to hide the huge impact of deforestation that took place before those years.

Of the 14.9 billion hectares of land on the planet, only 71% of it is habitable – the other 29% is either covered by ice and glaciers, or is barren land such as deserts, salt flats, or dunes. About 10,000 years ago, 57% of habitable land was covered by forest and 42% was covered by wild grassland and shrubs. In 2023, 45% of habitable land was used for agriculture, as illustrated by the image below.

People have been herding animals and burning or cutting down trees for thousands of years. While much of the forests could initially regrow, the result of people's activities was a strong increase in emissions of carbon dioxide, methane and black carbon.

While emission by people did accelerate since the start of the Industrial Revolution and even more recently, the rise in emission by people had already started thousands of years ago with growth in agriculture, herding of animals and associated deforestation, as illustrated by the combination image below, based on Ruddiman et al. (2015). The temperature has risen accordingly since those times.

[ from earlier post ]

Emission caused by people's activties include carbon dioxide, methane and black carbon. A 2013 study by Bond et al. calculates that black carbon has a warming effect of about 1.1 W/m², part of which is caused by black carbon darkening the snow and ice cover since pre-industrial times, as discussed on the aerosols page. By some calculations, the temperature in 1520 had risen by 0.29°C, compared to thousands of years earlier.

Emissions and Temperature Rise

The observed temperature rise (O) is actually masked by aerosols (M). As said, the IPCC only includes the rise from the period 1850-1900, ignoring the rise before the period 1850-1900 (P). Aerosols could fall out of the air soon, so when adding things up (E1+E2), the rise from pre-industrial (O+M+P) could be a lot more than what many believe it is.

When also taking into account that the temperature would have fallen naturally (i.e. in the absence of these emissions and in line with Milankovitch cycles, the rise caused by people to negate that could also be included (E3), adding up to an even higher historic temperature rise (O+M+P+H).

In addition, the (full) impact of emissions that occurred in the past may not be fully felt yet, e.g. the full effect of carbon dioxide emissions reaches its peak only a decade after emission (E4). Furthermore, humans are likely to continue to cause emissions in the near future (E5). Finally, additional releases of greenhouse gases are likely to come what was once called permafrost and as sinks turn into sources, resulting in an additional rise that's already baked into the cake (E6). Altogether, the full rise (total historic rise plus the near-future rise) could be the sum of O+M+P+H+F.

The diagram below further illustrates the importance of feedbacks and deforestation. Removal of trees has caused deforestation and soil carbon loss since prehistoric times, in turn causing emissions including carbon dioxide, methane and black carbon, while also reducing cooling aerosols released by trees and while also reducing the heat buffer of evaporation that previously cooled the atmosphere. Since prehistoric times, burning wood and deforestation has caused emissions of black carbon and dust that blackened the snow and ice cover, thus speeding up its decline.

[ from earlier post ]

The image below illustrates how much the temperature may have risen from pre-industrial times and how much potential there is for a 3°C rise as early as in 2026.

[ from earlier post ]

Climate Emergency Declaration

UN secretary-general António Guterres recently spoke about the need for “a credible global response plan to get us on track” regarding the international goal of limiting the global temperature rise. “The science demands action, the law commands it,” Guterres said, in reference to a recent international court of justice ruling. “The economics compel it and people are calling for it.”

What could be added is that the situation is dire and unacceptably dangerous, and the precautionary principle necessitates rapid, comprehensive and effective action to reduce the damage and to improve the outlook, where needed in combination with a Climate Emergency Declaration, as described in posts such as this 2022 post and this one and as discussed in the Climate Plan group.