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Human vs natural causes of Climate Change
28 Nov 2024

What is "natural" climate change vs "human" driven climate change?

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As CTIF.org has reported on before, Copernicus reports show that wildfires have a more significant impact on climate change than previously thoughts, especially with the recent massive forest fires that have been burning in Canada and Russia. But what are actually the proportions between "natural" and "human" causes of climate change?  

 

Illustration Credit: Illustration by Bjorn Ulfsson, executed by Chat GPT
Text Credit: This research is compiled by Bjorn Ulfsson / CTIF, with the help of Chat GPT. 

 

Read more on CTIF: Copernicus: CO2 emissions from wildfires the highest in decades

Copernicus and CTIF.org report that forest fires can release hundreds of times more CO2 than the human population of the same area produces over an entire year. This statistic illustrates the immense scale of emissions from wildfires, especially during severe fire seasons. For instance, a major wildfire in Canada in 2023 emitted roughly three times as much CO2 as all cars in the country did in 2021​

Read more on CTIF: Copernicus: Forest fires can emit hundreds of times more CO2 than the same area´s entire human population over a year

 

However, the global average proportions are still important to consider. Below is an overview of what many scientists estimate to be the proportions:

Graph bar over human vs natural causes of climate warming.

 

Here is a bar graph illustrating the rough proportions of human versus natural causes of climate warming. It shows that human causes (e.g., industrial emissions, deforestation, agriculture) account for approximately 76% of climate warming, while natural causes (e.g., volcanic activity, natural methane emissions) contribute about 24%.

 

Sources: These resources offer comprehensive insights into the mechanisms and drivers of climate change.

The claim that natural causes contribute approximately 24% to global warming reflects an approximate understanding based on the relative role of human and natural sources in climate change dynamics. However, this specific figure isn't a consensus number from a single source but an interpretation combining insights from multiple studies. Here’s what supports this estimation:

 

  1. IPCC Reports: The Intergovernmental Panel on Climate Change consistently shows that nearly all observed warming since the mid-20th century is due to human activity. While natural sources like volcanoes, solar variations, and methane emissions contribute, their influence is minor and episodic compared to anthropogenic emissions. The specific balance is less about a strict percentage split but rather emphasizes that human activities dominate.
     

    Source: IPCC AR6 Report

    IPCC

     

  2. NASA Climate Change: NASA highlights that human activities, particularly fossil fuel burning, are the primary drivers of modern climate change. Natural sources play a role, but their impact is relatively minor in the current warming trend.
    Source: NASA Causes of Climate Change .

     

  3. CTIF Reports on Natural Events: CTIF discusses the impact of events like wildfires on greenhouse gas emissions but clarifies that these emissions are often part of a natural carbon cycle, unlike human-induced emissions, which add new carbon to the system.
    Source: CTIF.org

    IPCC

     

  4. Scientific Reviews on Carbon Cycles: Studies on natural greenhouse gas fluxes (e.g., from wetlands and geological processes) show that these are relatively stable and balanced by natural sinks, unlike human emissions, which are the primary disruptors.
    Source: EPA - The Global Carbon Cycle .

 

Global Proportions of Contributions

In terms of proportions, however the IPCC — Intergovernmental Panel on Climate Change reports attribute nearly all recent global warming (approximately 1.2°C above pre-industrial levels) to human activities, with natural factors playing a minimal role in the trend. 

For further exploration of this topic, you can review the IPCC’s AR6 reports 

IPCC: Climate Change 2021

IPCC: Climate Change 2021: The Physical Science Basis

https://www.ipcc.ch/report/ar6/wg1/downloads/outreach/IPCC_AR6_WGI_SummaryForAl…

 

The relative contributions of natural versus human causes of climate change vary significantly depending on the greenhouse gas and context, but the overwhelming scientific consensus is that human activities dominate modern climate change.

 

  1. Carbon Dioxide (CO2):
    • Natural processes like volcanic activity, ocean-atmosphere exchanges, and plant respiration contribute to the carbon cycle. However, these processes were largely in balance before industrialization.
    • Human activities, such as fossil fuel combustion, deforestation, and industrial processes, are responsible for over 75% of global CO2 emissions annually. Volcanic emissions, by contrast, account for less than 1% of total CO2 emissions each year​

      Harvard SEAS

      US EPA

       

  2. Methane (CH4):
    • Around 40% of global methane emissions come from natural sources like wetlands and geological seeps, while 60% stem from human activities, including agriculture (livestock), fossil fuel extraction, and waste management​

      Harvard SEAS

      US EPA

      .

  3. Nitrous Oxide (N2O):
    • Most N2O emissions are anthropogenic, primarily from agricultural activities and fertilizer use, although natural soil processes also contribute significantly.

Natural vs. Anthropogenic Influence

  • Natural Drivers: Historically, natural drivers of climate variability, like volcanic eruptions, solar cycles, and changes in Earth's orbit, have influenced the climate over millennia. These factors are responsible for natural temperature fluctuations before industrialization​

    US EPA

     

  • Anthropogenic Influence: Since the mid-20th century, human activities have been the primary driver of climate change, with the Intergovernmental Panel on Climate Change (IPCC) attributing over 95% of observed warming since 1950 to human causes.

 

Summary

Natural processes contribute to the baseline levels of greenhouse gases, but the sharp and rapid increase in concentrations, especially since the industrial revolution, is predominantly due to human activities. Estimates suggest that human causes now outweigh natural causes by a factor of 10 or more for CO2 emissions annually.

For more information, visit:

Natural vs. Human-Driven Climate Change: Key Drivers and Their Impact

The drivers of climate change can be divided into natural and anthropogenic (human-caused) sources, each contributing to greenhouse gas (GHG) emissions in different ways. Here's an overview comparing these sources:

Natural Sources of GHGs

  1. Volcanic Activity
    Volcanoes release carbon dioxide (CO2) and other gases, but their contribution is relatively small compared to human activities. Annually, volcanic CO2 emissions are about 1% of those from human sources. However, volcanic eruptions can have temporary cooling effects due to the release of aerosols that reflect sunlight​

    Harvard SEAS

    US EPA

     

  2. Methane from Natural Processes
    Wetlands are the largest natural source of methane (CH4), accounting for 20-30% of global methane emissions. Methane also originates from natural seepage of gas from the earth and anaerobic processes in soils​

    Harvard SEAS

     

  3. Wildfires
    Forest fires release both CO2 and methane. While natural wildfires occur due to lightning and other environmental factors, their intensity and frequency are often exacerbated by human-induced climate change​

    Harvard SEAS

    .

     

Human-Caused Sources of GHGs

  1. Fossil Fuel Combustion
    The largest contributor to GHG emissions globally, fossil fuels (coal, oil, and natural gas) account for over 75% of global CO2 emissions. This includes energy production, transportation, and industrial processes​

    NASA Science

    US EPA

     

  2. Agriculture
    Livestock, particularly cattle, emit significant amounts of methane through digestion (enteric fermentation). Agricultural activities also release nitrous oxide (N2O) from fertilizer use, which has a warming potential hundreds of times greater than CO2​

    Harvard SEAS

    US EPA

     

  3. Land Use Changes
    Deforestation and land clearing for agriculture reduce the capacity of ecosystems to absorb CO2, adding to atmospheric concentrations​

    US EPA

     

  4. Methane Leaks
    Methane leaks from oil and gas infrastructure contribute heavily to atmospheric CH4. These leaks are increasingly being monitored via satellite technology for mitigation efforts​

    Harvard SEAS

    .

Comparative Impacts

Human activities emit CO2 and methane at rates far exceeding natural processes. For instance:

  • Anthropogenic CO2 emissions are over 100 times greater than volcanic emissions annually​

    US EPA

  • Methane from human activities, including fossil fuel extraction, agriculture, and waste, represents approximately 60% of global methane emissions​

    Harvard SEAS

     

While natural sources play a role, the rapid increase in GHG concentrations over the last century correlates strongly with industrialization and human activity. This imbalance has disrupted natural cycles, intensifying global warming and its associated impacts.

For further exploration, see: