Uploaded August 2026 | Updated September 2026, 2 weeks ago
How much of the observed rise in atmospheric CO₂ is caused by human emissions—and how much can be explained by temperature-dependent natural processes?
In this presentation, German physicist Hermann Harde examines the global carbon cycle and contrasts the IPCC’s explanation of increasing atmospheric CO₂ with his own approach.
Harde questions the assumption that the natural carbon cycle remained fixed at a pre-industrial equilibrium of approximately 280 ppm. He argues that natural emissions and absorption vary with temperature and that natural and anthropogenic CO₂ molecules must be treated equivalently within the carbon cycle.
He discusses:
• the IPCC carbon-cycle model and airborne fraction;
• residence time, adjustment time and effective absorption time;
• whether absorption is proportional to emissions or atmospheric concentration;
• the Bern carbon-cycle model and its multiple adjustment times;
• temperature-dependent emissions from soils, oceans and the biosphere;
• radiocarbon as a tracer of atmospheric carbon exchange;
• carbon-14 measurements following nuclear bomb tests;
• a three-reservoir model involving the stratosphere, troposphere and surface;
• the relationship between tropical temperatures and net CO₂ emissions;
• El Niño events and variations in the Mauna Loa record.
Using radiocarbon observations, Harde estimates an effective atmospheric absorption time of no more than approximately eight to ten years. His model attributes about 13 ppm—or roughly 9% of the atmospheric increase since 1850—to human emissions. He argues that the remainder can largely be explained by temperature-dependent natural emissions, particularly from tropical soils and the biosphere.
Harde also estimates that the anthropogenic contribution to industrial-era warming is approximately 0.3°C. He concludes that policies intended to reduce this relatively small contribution threaten energy security, economic prosperity and living standards.
The presentation concludes with a short discussion in which Ferdinand Engelbeen challenges Harde’s treatment of fossil-fuel emissions, carbon isotopes and the concentration differences that govern exchanges between the atmosphere and other carbon reservoirs.
Recorded during the Clintel Workshop on Recent Research Developments on Atmospheric Temperature, Carbon Dioxide and Their Relationship at the National Technical University of Athens on 19 September 2024.
This video was filmed, edited and produced by Aphroditi Katerinopoulou:
vimeo.com/user52800014
aphroditikat@yahoo.gr
Hermann Harde is a physicist formerly affiliated with Helmut Schmidt University in Hamburg, Germany.
Learn more about Clintel and the World Climate Declaration:
clintel.org
Hoofdstukken
00:00 Introduction
00:45 Opening remarks
03:13 The IPCC explanation of rising CO₂
05:14 The pre-industrial carbon balance
07:40 Residence time and the airborne fraction
09:15 Problems with conventional carbon-cycle models
11:13 Multiple adjustment times in the Bern model
12:35 A modified IPCC interpretation
16:00 Harde’s approach to the carbon cycle
19:07 Radiocarbon as a tracer
20:12 Carbon-14 and nuclear bomb tests
21:44 A multi-reservoir carbon model
23:15 Modelling radiocarbon decay
26:16 Applying the model to human emissions
28:17 Estimating the anthropogenic contribution
28:46 Temperature-dependent natural emissions
30:43 Analysing the Mauna Loa record
32:53 Tropical temperatures and El Niño
34:31 Soil respiration and ocean outgassing
35:27 Temperature, emissions and phase relationships
36:43 Comparing calculated and measured CO₂
37:53 Is only 9% of the increase anthropogenic?
39:11 Historical CO₂ measurements
40:30 Conclusions
42:08 Questions and discussion
42:47 Ferdinand Engelbeen challenges the model
How much of the observed rise in atmospheric CO₂ is caused by human emissions—and how much can be explained by temperature-dependent natural processes?
In this presentation, German physicist Hermann Harde examines the global carbon cycle and contrasts the IPCC’s explanation of increasing atmospheric CO₂ with his own approach.
Harde questions the assumption that the natural carbon cycle remained fixed at a pre-industrial equilibrium of approximately 280 ppm. He argues that natural emissions and absorption vary with temperature and that natural and anthropogenic CO₂ molecules must be treated equivalently within the carbon cycle.
He discusses:
• the IPCC carbon-cycle model and airborne fraction;
• residence time, adjustment time and effective absorption time;
• whether absorption is proportional to emissions or atmospheric concentration;
• the Bern carbon-cycle model and its multiple adjustment times;
• temperature-dependent emissions from soils, oceans and the biosphere;
• radiocarbon as a tracer of atmospheric carbon exchange;
• carbon-14 measurements following nuclear bomb tests;
• a three-reservoir model involving the stratosphere, troposphere and surface;
• the relationship between tropical temperatures and net CO₂ emissions;
• El Niño events and variations in the Mauna Loa record.
Using radiocarbon observations, Harde estimates an effective atmospheric absorption time of no more than approximately eight to ten years. His model attributes about 13 ppm—or roughly 9% of the atmospheric increase since 1850—to human emissions. He argues that the remainder can largely be explained by temperature-dependent natural emissions, particularly from tropical soils and the biosphere.
Harde also estimates that the anthropogenic contribution to industrial-era warming is approximately 0.3°C. He concludes that policies intended to reduce this relatively small contribution threaten energy security, economic prosperity and living standards.
The presentation concludes with a short discussion in which Ferdinand Engelbeen challenges Harde’s treatment of fossil-fuel emissions, carbon isotopes and the concentration differences that govern exchanges between the atmosphere and other carbon reservoirs.
Recorded during the Clintel Workshop on Recent Research Developments on Atmospheric Temperature, Carbon Dioxide and Their Relationship at the National Technical University of Athens on 19 September 2024.
This video was filmed, edited and produced by Aphroditi Katerinopoulou:
vimeo.com/user52800014
aphroditikat@yahoo.gr
Hermann Harde is a physicist formerly affiliated with Helmut Schmidt University in Hamburg, Germany.
Learn more about Clintel and the World Climate Declaration:
clintel.org
Hoofdstukken
00:00 Introduction
00:45 Opening remarks
03:13 The IPCC explanation of rising CO₂
05:14 The pre-industrial carbon balance
07:40 Residence time and the airborne fraction
09:15 Problems with conventional carbon-cycle models
11:13 Multiple adjustment times in the Bern model
12:35 A modified IPCC interpretation
16:00 Harde’s approach to the carbon cycle
19:07 Radiocarbon as a tracer
20:12 Carbon-14 and nuclear bomb tests
21:44 A multi-reservoir carbon model
23:15 Modelling radiocarbon decay
26:16 Applying the model to human emissions
28:17 Estimating the anthropogenic contribution
28:46 Temperature-dependent natural emissions
30:43 Analysing the Mauna Loa record
32:53 Tropical temperatures and El Niño
34:31 Soil respiration and ocean outgassing
35:27 Temperature, emissions and phase relationships
36:43 Comparing calculated and measured CO₂
37:53 Is only 9% of the increase anthropogenic?
39:11 Historical CO₂ measurements
40:30 Conclusions
42:08 Questions and discussion
42:47 Ferdinand Engelbeen challenges the model
