Understanding the causes of global warming and climate change myths

In recent decades, climate change denial has declined as its effects have become more visible. However, the tendency towards denial still exists and even seems to be increasing in some places or changing. Misunderstandings and misinformation about the causes and nature of climate change still exist, often driven by ideas about natural fluctuations in the Earth's climate. To better understand what is causing modern climate change, it is useful to examine the main factors that determine the temperature of the planet and to assess whether changes in these factors can explain the warming of recent decades.

Main factors influencing Earth's climate

1. Distance from the Sun

The closer a planet is to its star, the more thermal energy it receives. Earth is in a so-called "habitable orbit," which allows liquid water and conditions that are suitable for life to exist. Distance from the sun has not changed historically and therefore cannot explain current warming.

2. Solar radiation and solar oscillations

The Sun changes its energy output slightly in cycles of about 11 years, as well as longer cycles such as the 22-year geomagnetic cycle. However, these fluctuations are too small to explain the major long-term fluctuations now observed in the climate. Satellite measurements dating back to the 1970s show that total solar radiation has not increased in line with the warming that has occurred. Recent measurements also confirm a fairly stable 11-year average solar output, while the Earth's average temperature continues to rise.

3. Stærð plánetunnar 

Massi og þyngdarkraftur Jarðarinnar hefur áhrif á getu hennar til að halda lofthjúpi, sem er grundvallaratriði í hitastjórnun. Massi Jarðar hefur nánast ekkert breyst og hefur því enga þýðingu í nýlegum hlýnunaráhrifum. 

4. Þykkt og efnasamsetning lofthjúpsins 

The greenhouse effect, mainly due to gases such as carbon dioxide (CO₂), methane (CH₄), and water vapor (H₂O), largely determines how much heat is retained at the surface. Recent data show a significant increase in CO₂ from human activities, which is the main driver of current warming. Other long-lived greenhouse gases (such as nitrous oxide (N₂O) and various fluorinated gases) also play a role, although CO₂ is the most influential.

5. Earth's orbit (central declination, orbital inclination, and polar rotation)

Small changes in the Earth's orbit (Milankovitch oscillations) affect the distribution of solar energy over thousands of years and cause natural climate fluctuations (eg ice ages). These long-term fluctuations cannot explain the rapid warming of today, which has occurred in just a few decades.

6. Earth's magnetic field

Segulsviðið verndar Jörðina gegn sólvindum og geimgeislum, sem að einhverju leyti geta haft áhrif á efnahvörf í lofthjúpnum. Hins vegar hafa breytingar á segulsviðinu verið litlar og fylgja ekki núverandi hækkun hitastigs. Sumir halda því fram að geimgeislar, sem segulsviðið stýrir, valdi tíðari skýjamyndun og kólnun, en rannsóknir sýna að slík áhrif eru hvergi nærri nægjanleg til að skýra núverandi hlýnun. 

7. Location of continents and ocean currents

The arrangement of continents affects the ocean currents that transport heat around the globe. In the time of the dinosaurs, the continents were arranged differently, which created very different climate patterns. However, mountain ranges, landslips, and crustal movements occur over millions of years, so minor changes in the present cannot explain the rapid climate changes of recent decades. Changes in land use (such as deforestation) can affect regional reflectance (albedo) and the water cycle, but are not sufficient to explain global warming.

8. Endurkast (albedo) 

The reflectivity of the Earth's surface affects how much radiation is reflected. Ice sheets, snow, and clouds increase reflectivity (albedo), while dark areas such as forests and oceans absorb more heat. Melting ice reduces reflectivity, thus increasing warming. However, this is a consequence of warming rather than its primary cause.

9. Volcanic activity

Large volcanic eruptions can eject sulfur dioxide into the stratosphere, causing temporary cooling by reflecting solar radiation. However, CO₂ emissions from volcanic eruptions are negligible compared to human emissions, and recent volcanic activity is not sufficient to explain the warming that is occurring.

10. Particulate matter and particles

Pollution from industry and natural disasters (e.g. forest fires) can reduce radiation through particulate matter, which either cools (reflects radiation) or warms (absorbs radiation). Such materials have probably reduced warming somewhat, especially in the mid-20th century, but not enough to offset the rapid increase in greenhouse gases. As air pollution decreases (e.g. through better technology), this "cooling offset" could be reduced, leading to warmer weather than would otherwise be the case. Despite this, it is clear that the massive CO₂ emissions outweigh the mitigating effects of particulate matter.

11. Water vapor

Water vapor is certainly a powerful greenhouse gas, but its amount is generally determined by temperature. Warming caused by CO₂ increases moisture in the atmosphere, which multiplies the warming effect. However, water vapor is more of a response to temperature change than the initial driving force. CO₂ is therefore sometimes called the “control switch” of the climate, because changing levels of CO₂ trigger the initial warming, which in turn increases water vapor in the atmosphere.

The greenhouse effect

Gróðurhúsaáhrifin eru grundvallarferli í lofthjúpi Jarðar, þar sem ákveðnar lofttegundir gleypa og endurkasta innrauðri varmageislun, sem hægir á varmatapi frá yfirborðinu út í geiminn og stuðlar þannig að lífvænu hitastigi. Sólargeislun í sýnilegum og útfjólubláum bylgjulengdum nær í gegnum lofthjúpinn og hitar yfirborð Jarðar. Yfirborðið endurkastar þessum varma sem innrauðri geislun, sem CO₂, CH₄, N₂O og aðrar gróðurhúsalofttegundir taka upp og geisla aftur í allar áttir. Þetta tefur flótta varmans út í geiminn og veldur því að neðra lofthvolfið hlýnar. Lögmál eðlisfræði (t.d. skammtafræði og litrófsmælingar) styðja þessa skýringu, sem sýnir hvers vegna aukning gróðurhúsalofttegunda leiðir til meiri hlýnunar. 

Recent changes in CO₂ and temperature: What the data shows

Since the Industrial Revolution, atmospheric CO₂ concentrations have increased from about 280 ppm (parts per million) to over 420 ppm. This increase is accompanied by an increase in the Earth's average temperature, which has risen by about 1.2°C since the end of the 19th century.

The speed of this development is unprecedented compared to natural fluctuations over the past millennia to millions of years. Studies of ice cores, tree rings and sediments clearly show that such a rapid increase in CO₂ and temperature has not been observed before. For example, data from periods such as the “Paleocene–Eocene Thermal Maximum” (PETM) suggest that the current changes are many times faster than most previous large-scale climate fluctuations.