They’re blamed for causing an increase in global warming, but they also play a key role in the energy balance of the planet. They cause the greenhouse effect and among the most known ones are carbon dioxide, methane, and nitrous oxide. They are the greenhouse gases.

Simply put, greenhouse gases are gases in the Earth’s atmosphere that trap heat. They let solar energy pass through, but then they capture the heat inside the atmosphere.

Greenhouse gases are found in low concentrations in the atmosphere (and have been around for millions of years), but the proportion has ramped up since the beginning of the industrial revolution. Man-made activity (primarily coming from industrial activity, but also from agriculture and transportation) has caused a sharp increase in greenhouse gases, which in turn are trapping more heat and causing temperatures to rise. This is why greenhouse gases are linked with man-made global warming.

But let’s take it one step at a time.

What’s the greenhouse effect?

The greenhouse effect was identified by scientists in 1896. It’s the natural warming of the planet that happens as gases in the atmosphere trap heat from the sun, which would otherwise leave for space.

Up to 30% of the solar energy that arrives into the planet is reflected back to space, while the other 70% enters the surface through the atmosphere and is absorbed by the atmosphere, the land, and the oceans and heat the planets.

The heat is transformed into invisible infrared light. Some of it goes to space, while most of it is absorbed by greenhouse gases and cause more warming. The concentration of gases in the atmosphere was about 200 parts per million for a large part of the last 800.000 years.

While the exact model is very complex, and the numbers are sometimes hard to pinpoint accurately, the greenhouse effect is well-known for more than a century. It is supported by irrefutable scientific evidence and in principle, it is quite easy to grasp. Most kids learn it in school.

What are the main greenhouse gases?

There are a group of gases that are responsible for the greenhouse effect, including carbon dioxide, methane, nitrous dioxide, water vapor, and fluorinated gases. They have different chemical properties and can gradually increase or decrease from the atmosphere through different processes. The one process that is most pressing at the moment (and has been for the past century) is human activity.

Carbon dioxide (CO₂) accounts for 76% of the global human-caused emissions. After being released into the atmosphere, about 40% stays for 100 years, while 20% remains after 1,000 years and 10% up to 10,000 years later.

Meanwhile, methane (CH₄) stays for less time in the atmosphere than carbon dioxide but it’s much stronger in terms of the greenhouse gas effect. Its global warming impact is 25 times larger than the one of the carbon dioxides in a period of 100 years. It accounts for 16% of man-made greenhouse gas emissions.

Nitrous oxide (N₂O) is also a powerful gas, with a global warming potential of 300 times more than carbon dioxide on a 100-year time scale. It stays on the atmosphere for more than a century and it represents 6% of the man-made greenhouse gas emissions worldwide.

Fluorinated gases are a group of gases caused by human activities from different industrial and manufacturing processes. They are grouped into nitrogen trifluoride (NF₃), sulfur hexafluoride (SF₆), perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs).

They only account for 2% of the greenhouse gas emissions caused by humans but they trap much more heat. Their global warming potential is considerably high, and they have a long atmospheric lifetime. HFCs replaced chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) but are now tried to be phased out because of their global warming potential.

Finally, water vapor is considered the most abundant greenhouse gas. It’s not linked to human activities directly, but can also result from other greenhouse gases issued by man. In a constant feedback loop, more water absorbs more heat, leading to larger global warming.

Why are there changes in greenhouse gases now?

The Intergovernmental Panel on Climate Change (IPCC) argues that there are a set of factors that can drive greenhouse gas emissions. In principle, they are influenced by economic activity, energy use, technology, and land-use patterns.

Burning coal, oil and natural gas to create electricity represent one-quarter of the global man-made emissions. It’s the most important single source. Such activities were responsible for 27.5% of the emissions in the US in 2017. The main greenhouse gas released because it is carbon dioxide, with smaller amounts of methane and nitrous oxide also being released in the process.

Another quarter of the greenhouse gas emissions comes from agriculture and land-use activities like deforestation. Raising livestock and harvesting crops meant 8.4% of the emissions in the US in 2017. Most of the gases released were methane, produced mainly as cows belch and pass gas, and nitrous oxide, caused by fertilizers.

All trees, the plants, and the soil have the capacity to absorb carbon dioxide from the air. In the case of plants and trees, this is done through photosynthesis. Land-use changes such as deforestation, reforestation or afforestation can increase the level of carbon in the atmosphere or decrease it by removing or absorbing CO2.

One-fifth of the global man-made emissions are generated by the industrial sector, caused by activities such as manufacturing of goods and raw materials such as cement and steel, food processing and construction. In the US, 22.4% of the man-made emissions in 2017 came from the industrial sector. Most of it was CO2, followed by methane, nitrous oxide and fluorinated gases.

Transportation also plays a key role, as burning fossil fuels to power transportation systems represent 14% of the global man-made emissions. In the US, the transportation sector is the main contributor of all greenhouse gases. Carbon dioxide is the main gas released in the sector, followed by methane and nitrous oxide. Cars and trucks explain 80% of the emissions of the transportation sector in the US.

Finally, managing buildings around the world lead to 6.4% of global emissions. Homes and businesses account for 11% of the emissions in the US, made up of carbon dioxide and methane cause of burning fossil fuels for heating and cooking. There are also other sources from waste management and leaking refrigerants.

Those are the main sources of man-made greenhouse gas emissions currently ongoing in the world.

What are the consequences of the release of more gases?

Greenhouse gas emissions caused by human activities are higher than ever. Concentrations are growing every year and the planet is heating up. The planet’s average temperature has increased over one degree Celsius since pre-industrial times, with two-thirds of the warming that has occurred in just the last few decades.

All five of the years between 2014 and 2018 have been the hottest on record globally, according to the World Meteorological Organization. While countries have submitted plans to reduce their climate footprint, they are far from ambitious and would lead to the temperature keep rising.

But then again, that’s the big deal — why is global heating so bad?

Man-made global warming alters the Earth’s climate system in numerous ways. It causes more frequent and intense extreme weather events such as heatwaves and hurricanes, it exacerbates precipitation extremes, making for example dry regions drier and it alters ecosystems and natural habitats, changing the geographical ranges and seasonal activities. Research has shown that hurricanes are bigger and stronger due to climate change, drought is also much more common, and wildfires are also heavily accentuated by climate change. These are all events taking place now, costing a lot of money and putting people’s health (and even lives) at risk.

Sea level rise is also a major consequence of climate change. Two phenomena are at play here: the first and most significant one is melting ice at the poles, which ends up in the global oceans and causes sea level rise. The second is thermal expansion caused by rising temperatures, and this can also contribute to sea level rise. These phenomena are not set to happen at some point in the distant future — they are taking place right now. Entire families on low-lying islands have been forced to relocate as their homes are slowly swallowed by rising seas.

All ecosystems are also affected by climate change. The bleaching of corals, the forcing of creatures out of their historical habitats and the warming of ocean temperatures are all taking place right now, with dangerous and long-lasting consequences.

A warmer world not only affects the natural world but also mankind. Insects that spread diseases such as Zika do better in higher temperatures, arriving in regions that weren’t previously affected. Doctors and researchers all around the world agree that climate change brings in new (and potentially devastating) health risks.

Food supply could also be reduced due to floods and droughts, as crop yields could see a reduction. These are just a handful of consequences, and just things that are happening now. If the concentration of greenhouse gases continues to grow, the consequences will certainly be dramatic.

All in all, this climate change can usher in some huge changes, and it comes with a price we can probably not afford to pay.

So, what’s the solution?

The planet has experienced warming and cooling periods many time in its geologic history. Driven by natural forces, these changes generally took place over millions of years, or at the very worst, thousands of years. Life had time to adapt, and even so, dramatic changes tended to bring dramatic loss of life and biodiversity. Life can presumably bounce back from even dramatic climate events, but whether or not humans can also survive is a different (and much more difficult question).

But unlike previous events, today’s warming is happening at a speed that can’t be linked just to natural causes. There is a mountain of evidence showing that human activities are to blame — but they can also bring a solution.

Scientists have documented the main sources of greenhouse gases, and they’ve also proposed ways to reduce our climate footprint — but the challenge is big. It would require aggressive and fast action, aiming at a carbon-neutral world as soon as 2050. For that to happen, fossil fuel production and consumption have to be stopped as well as deforestation. In addition to developing more renewable energy sources, we also have to keep as much oil and coal in the ground and not burn. We need to develop sustainable food systems, clean transportation, and greener construction materials. We need systemic changes at all levels of society, especially at the policy level.

The 2015 Paris Agreement is a good first step. The pact recommends action to ensure that we reduce emissions and keep warming within two degrees Celsius above pre-industrial (with an extra goal of 1.5 Celsius degrees). Doing so would significantly reduce the consequences of global warming. But we’re not even on course for that to happen. More effort and ambition is needed from all countries if we want to keep greenhouse gases under control. Otherwise, we have to be prepared to pay the price.