Nordell published a controversial explanation to global warming in 2003 (Thermal Pollution Causes Global Warming, Global and Planetary Change. Vol. 38, Issue: 3-4, p. 305-312.). Since it has not been possible to get external funding for this idea most of the work was carried out during a long time as a "hobby research" with the assistance of helpful and interested students.

In this study global mean temperatures were used to calculate Earth's energy balance. On this time scale our planet does not get any net heating from the sun since incoming solar radiation is emitted at exactly the same rate. Consequently, Earth is not heated by the sun. Our planet is in fact a heat source in space to which it emits its net heat. The only major global net heat source is the geothermal heat flow from the interior of the planet. Other natural heat net sources are heat emitted from volcano eruptions, meteorites, etc.

Before global warming, around 1880, Earth was in thermal equilibrium at a mean temperature of 13.6C. At this temperature the geothermal heat flow was emitted to space as outgoing long-wave radiation (OLR). The OLR is driven by the temperature difference between the ground surface and the atmosphere.

Since the start of global warming the global mean temperature has increased from 13.6C to 14.3 (1999) which means that also the OLR has increased. This additional OLR requires that a new global net heat source. This heat source is the heat dissipation resulting from the global use of non-renewable energy, which thus has caused the global warming.

The total non-renewable energy consumption since 1880 has dissipated into heat of which a small part has been emitted to space. The remaining heat has shown as global warming. Consequently, this energy must match the energy required to cause occurring warming of air, ground water. This is the focus of my present work. Preliminary calculations of stored energy in air, ground and water seem to agree very well with accumulated net heat generation during the last 120 years.

A popular version of the global warming explanation was published April 2004 in the Swedish HVAC Journal of Energy & Environment (Energi & Miljö).   In a recent study, the global warming was defined as the global heat accumulation in air, ground and water since 1880.  

 · Heat accumulation in the air means the amount of heat required to warm up the air to the degree that has already happened and also the latent heat of the air humidity increase.
· Heat accumulation in the ground is caused by the increasing surface temperature which blocks the geothermal heat flow.
· Heat accumulation in water is based on the temperature increase of sea water which is uncertain and varies with a factor of ten in published scientific papers. Here, also the melting of land ice and sea ice are included.  

By comparing the net heat emissions with globally accumulated heat it shows that 55% of the global warming is explained by net heat emissions from the global use of commercial energy.  

Ongoing research aims to estimate the consumption of non-commercial energy. Such heat origin from several sources; e.g. gas flaring at oil fields, underground coal fires, peat fires, oil used for plastic production, and also the large-scale deforestation that has occurred during the last century. This “renewable” energy source contributes to the net heating since the use of wood considerably exceeds the growth.

Above mentioned explanation to global warming was presented at the Global Conference for Global Warming, Istanbul 6-10 Juli 2008, a paper that won the Best Paper Award.