At a global level

But... hasn’t Earth survived many episodes of climate change? Why should we be worried?

The answer to this question is made up of various arguments that complement one another:

  • Because this is the first climate change caused by human activity, while the previous episodes were the result of natural causes.
  • Because this is the fastest climate change ever experienced on Earth.
  • Because it is causing an increase in average temperatures which has clear and serious effects on ecosystems and people.
  • Because it is unjust and causes inequalities. Not all countries are equally responsible for generating greenhouse gases, and not all countries have the same capacity to adapt. In fact, the countries most affected and with the greatest difficulties adapting to the changes are those that have contributed least to the problem. It is therefore a problem that goes beyond strictly environmental aspects to become a question of ethics and responsibility.

When we talk about greenhouse gases, are we just talking about CO2? How are these gases measured?

To measure the gases causing the current climate change, we use a standardised measure which is CO2 equivalent. Each of the greenhouse gases has a global warming potential that indicates the capacity it has to contribute to such warming. The values are as follows: 1 CO2, 25 CH4 and 298 N2O. Giving a final formula of: CO2 + 25xCH4 + 298xN2O = CO2 eq. So, while we normally talk about x tonnes of CO2, in reality we are referring to CO2 eq.

Which are the greenhouse gases?

Greenhouse gases are found naturally in the atmosphere, although human activity has increased their concentration. They are as follows:

  • Carbon dioxide (CO2): produced in large quantities in forest fires and volcanic eruptions. The current excess is due to the use of fossil fuels (oil, coal and natural gas) for energy and their use in vehicles, heating, thermal power stations, industry etc. 
  • Methane (CH4): generated as a result of agricultural and livestock activity. Also in landfills, and in wetlands and marshes.
  • Nitrogen oxide: released by crop fertilisers, excrement and livestock.
  • Water vapour.
  • Gases originating directly from human activity: chlorofluorocarbons (CFCs) from industry, used in air conditioning systems, aerosols, extinguishers etc., and sulphur hexafluoride.


So greenhouse gases are polluting gases?

The presence of CO2 and other greenhouse gases in the atmosphere is natural and, in fact, it is one of the things that makes life possible on Earth, as it keeps the planet at the right temperature. The concentration of these gases is the result of a balance between emissions sources and sinks (processes that absorb or fix the gases).

The problem is not whether or not these substances are pollutants, but the fact that we are increasing the concentrations of them and, thus, their capacity to retain the heat reflected by the Earth. Since the industrial revolution, anthropogenic sources have increased significantly, whilst the majority of sinks (oceans, vegetation, rocks, etc.) have much slower cycles. Current emissions may, therefore, take decades or centuries to be absorbed.

The use of fossil fuels has generated both this global warming and the increase in atmospheric pollution and, consequently, worse air quality. Climate change is a global phenomenon, while pollution acts more at a local level when the excessive emission of certain gases causes them to accumulate in concentrations that have a harmful effect on our health. These are nitrogen oxide and suspended particles.

Lastly, when we refer to ozone, we also need to differentiate between:

  • the loss of the ozone layer in the stratosphere (considered to be ‘good’ ozone at high altitudes, which makes plant and animal life on Earth possible thanks to the absorption of UV radiation), linked to the use of chlorine compounds such as aerosols, refrigerants and so forth;
  • and the presence of tropospheric ozone in the city (considered to be ‘bad’ ozone at low altitudes, which causes irritation and harms plants and animals due to its oxidising power, and which is also a greenhouse gas). This ozone forms when the nitrogen oxide gases from industrial and vehicle emissions react with volatile organic compounds (carbon found in chemical products that evaporate easily into the air, such as solvents in paint). 

Greenhouse effect, global warming, climate change... are they all the same thing?

The greenhouse effect is a natural phenomenon that supports life on Earth. It is related to the absorption capacity, the percentage of solar radiation reflected in the form of heat and its retention in the atmosphere by greenhouse gases (CO2, N2O, CH4), which represent 1% of the atmosphere’s composition. Increased emissions of these gases due to human activity produces global warming, increasing the average temperature of the planet (currently 15°C) and, as a consequence, causes changes in the climate and other effects:

  • Reduced snow and ice (increasing albedo).
  • Increased ocean temperatures (reduced sink capacity).
  • Ocean acidification.
  • Rising sea level.
  • Increases in extreme weather events.

To clarify the relationship between these concepts, it can be said then that the imbalance generated in the composition of the atmosphere is what causes the warming, and this aspect is resulting in climate change all over the planet.

Is it possible to be carbon neutral or ‘zero’ CO2?

Any activity that uses energy not produced from renewable sources (solar, wind, etc.) generates CO2 emissions. Some agricultural and livestock activities also generate greenhouse gas emissions. Therefore, it is still extremely difficult to find ‘zero emission’ products or services, unless they require no energy or this energy comes from renewable sources. What we can do, however, is offset these emissions by calculating the amount of greenhouse gases emitted in manufacturing a product or conducting an activity (for example, an aeroplane journey) and invest in a project that enables us to reduce emissions by the same amount.

Carbon footprint, ecological rucksack, ecological footprint... are they the same? What do labels tell us?

The carbon footprint of a product is the calculation of the emissions (of carbon) associated with its production from the extraction of the raw materials to the end of its useful life. It is therefore a calculation of the grams of CO2eq associated with the existence of the product or service in question.

In contrast, when we talk about the ecological footprint, we are referring to the amount of land required to support the needs of a person, community, society and so on. And in the case of ecological rucksack, this also takes into account other elements, such as water consumption, pollutant emissions, land use etc.

What is the Paris Agreement?

The Paris Agreement corresponds to the 21st session of the Conference of the Parties (COP) and the 11th session of the Conference of the Parties Serving as the Meeting of the Parties to the Kyoto Protocol (CMP 11), which was held from 30 November to 12 December 2015 in Paris, France.

The United Nations Climate Change Conference concluded with the adoption of an historic agreement to combat climate change and promote measures and investment for a low-carbon, resilient and sustainable future.

The aim of the Paris Agreement is to keep the increase in global average temperature this century to well below 2ºC and strengthen countries’ ability to deal with the impacts of climate change.

The results of the Conference of the Parties (COP 21) covered crucial areas considered to be essential for climate policy:

  • Mitigation: a rapid reduction in emissions to achieve the target temperature.
  • A global transparency and accountability system for climate action.
  • Adaptation: strengthen countries’ ability to deal with the impacts of climate change. 
  • Loss and damage: strengthen their ability to recover from climate impacts. 
  • Support: including finance, for nations to build clean, resilient futures.

Further information:


Are renewable energies the solution?

Renewable energies are a fundamental pillar to reduce the emissions generated by the energy system. However, given the need to rapidly speed up the rate at which emissions are cut, there are other aspects that also need to be addressed, such as:

  • The food production system, since agriculture and livestock account for a large part of methane and nitrogen oxide emissions, which are currently increasing much faster than CO2;
  • Maintaining and regenerating the world’s forests;
  • Transforming the social system on a scale similar to that of technological changes in order to achieve the mitigation levels needed. This includes the way in which we work, how we move around and what we eat, among other aspects.


Barcelona and the Climate Plan

What can a city like Barcelona do in response to a global problem like climate change?

Cities are part of the climate change problem, as the majority of emissions and energy consumption are concentrated in cities around the world, but for that reason they are also a key part of the solution.

In general terms, the majority of cities are already experiencing the impacts associated with climate change, such as effects on health, increasing temperatures, aggravation of the urban heat island effect, more periods of drought, more flooding, more heat waves, rising sea levels, reduction in water resources, etc. Local government measures are crucial to managing climate change issues, both on a local scale, because they increase the quality of life of city residents, and on a global scale, since the world’s urban populations make up over 54% of the planet’s inhabitants. In the European Union, 74% of the population lives in urban areas, consuming 75% of the energy.

Cities and their metropolitan surroundings demonstrate a close link between urbanisation, energy use and greenhouse gas emissions. Urban density and layout are key factors in influencing energy consumption, especially in the transport and construction industries.


Which sector could have the greatest impact in terms of mitigating climate change?

The transport and mobility sector is the main emitter of greenhouse gases and where our efforts mainly need to be focused. Reducing motorised mobility and moving towards alternative forms of transport, particularly public transport, and increasing the number of journeys made on foot and by bicycle are areas in which the fastest and most significant results can be achieved. Residential, retail and service buildings also account for a significant proportion of energy consumption and emissions. Improving the energy efficiency of buildings is another priority action we need to push ahead with.

Further information​

What are the biggest challenges that Barcelona will have to face in relation to climate change?

An increase in the number of heat waves and reduced availability of water for consumption. There will be more heat waves and they will also be more intense and longer lasting. Night-time temperatures will go up too, particularly in neighbourhoods near the coast. The first challenge to tackle is the heat waves. In the last 34 years, there have been eight such episodes in the city. The most intense of these was in 1982 but the longest occurred in 2003, lasting for 13 days.

Night-time temperature increases may cause problems for people's rest and recuperation. The neighbourhoods closest to the coast might be the worst affected by the increase in night-time temperatures. These increases could have consequences for people's health, as the nocturnal period of rest is the time when people recover from the whole day.

On the other hand, by 2050 it is anticipated that there will be a reduction in the availability of water resources and that demand will have increased by 4%. The city will need an additional 18 hm3 of water per year.

Further information

What are the biggest climate justice challenges that Barcelona will have to face in relation to climate change?

From the perspective of climate justice, the most important challenges posed by climate change will be tackling energy poverty, health problems linked to heat waves and increasing food prices. With climate change, and given the demographic and socio-economic dynamics of the city, the population most vulnerable to energy poverty will increase in size.

Although the future forecasts talk about a reduction in energy demand for heating buildings, the demand for energy and water supplies will increase with climate change (ventilation and refrigeration systems, personal hygiene and laundry). Households will have to deal with the higher costs of meeting their demand for electricity and water (not gas). In the coming years, there will be an increase in the number of households with dependent children and single-person households due to the growth in migratory movements and the ageing population.

In short, energy poverty will have to be redefined with climate change: there will be a fall in energy demand for heating but an increased demand for water and electricity for ventilation and climate control in buildings. The population most vulnerable to energy poverty will increase in size, given the demographic and socio-economic dynamics of the city.