Que países contaminan más y que países lideran las soluciones

Global energy-related CO2 emissions reached 37.4 billion tonnes in 2023, a historic record that confirms the insufficiency of measures adopted to date (IEA, CO2 Emissions in 2023). China leads in absolute terms with 12.7 billion tCO2 (30.7% of the global total), followed by the United States with 4.9 billion (11.8%), the EU-27 with 2.7 billion (6.5%), India with 2.9 billion (7.0%), and Russia with 1.8 billion (4.4%). These five actors account for 60.4% of global emissions. However, absolute emissions conceal fundamental demographic differences: China has 1.425 billion inhabitants compared to 335 million in the United States, meaning the average American emits 14.6 tCO2/year versus 8.9 tCO2 for the average Chinese citizen. The Persian Gulf countries have the highest per capita emissions on the planet: Qatar with 35.6 tCO2/inhabitant, Bahrain with 25.7, and Kuwait with 24.3, driven by the energy intensity of desalination, air conditioning, and the petrochemical industry.

The building sector is responsible for 37% of global CO2 emissions when both operational emissions (28%) and those embodied in construction materials (9%) are included, according to the Global Status Report for Buildings and Construction (UNEP, 2023). In absolute terms, China generates 5.2 billion tCO2 related to buildings (operation + materials), the United States 1.8 billion, and India 1.1 billion. Per capita building sector emissions reveal distinct patterns: an American generates 5.4 tCO2/year from building operations (natural gas heating, air conditioning, appliances), an average European 2.1 tCO2, and an Indian 0.8 tCO2. Australia (4.8 tCO2/inhabitant from buildings), Canada (4.5), and Saudi Arabia (5.1) even surpass the United States in this indicator, reflecting extreme climates, low efficiency of the building stock, and electricity mixes dependent on fossil fuels (natural gas 38% in Australia, oil 55% in Saudi Arabia).

The debate over who pollutes the most requires consideration of cumulative emissions since the start of the industrial era. Between 1850 and 2023, the United States emitted 422 billion tCO2 (24.5% of the global cumulative total), the EU-27 280 billion (16.3%), China 290 billion (16.8%), Russia 115 billion (6.7%), and the United Kingdom 78 billion (4.5%) (Our World in Data/Global Carbon Project, 2024). On a cumulative per capita basis, the United Kingdom leads with 1,150 tCO2/inhabitant since 1850, followed by the United States with 1,260 tCO2, while India barely reaches 34 tCO2/inhabitant and sub-Saharan African countries 8-15 tCO2. This historical asymmetry underpins the principle of common but differentiated responsibilities in the Paris Agreement and explains tensions in climate negotiations: developing countries demand climate financing of 100 billion USD/year (the Copenhagen 2009 commitment, fulfilled in 2022 with a two-year delay) to transition toward low-carbon models without repeating the emissions trajectory of industrialized economies.

Emissions embodied in international trade (carbon leakage) add another layer of complexity. China exports between 1,200 and 1,800 million tCO2/year embedded in manufactured products consumed in Europe, the United States, and Japan (Peters et al., 2012). When emissions are reassigned to the consuming country rather than the producer, the EU's carbon footprint increases by 15-20% and China's decreases by 10-15%. In the construction sector, this transfer is particularly relevant: 60% of steel consumed in the EU comes from imports (mainly Turkey, India, and China), and 45% of aluminum. The EU's Carbon Border Adjustment Mechanism (CBAM), operational since October 2023, places a price on the carbon embedded in imports of cement, steel, aluminum, electricity, fertilizers, and hydrogen, matching the cost of the European ETS (65-90 EUR/tCO2 in 2023) and partially closing this accounting gap.

Denmark has reduced its building sector emissions by 55% since 2005, combining building standards among the most stringent in the world (maximum primary energy demand of 20 kWh/m2 per year for new buildings since 2020), a district heating system covering 64% of households with heat sourced 70% from renewables and waste, and a ban on gas and oil boilers in new construction since 2013 (Danish Energy Agency, 2023). Sweden has radically decarbonized its residential heating: heat pumps supply 43% of heating energy, district heating (biomass + waste) 37%, and direct electricity 12%, leaving fossil gas with barely a 0.5% share. Swedish residential sector emissions fell by 42% between 2005 and 2022 (Swedish Energy Agency, 2023). Norway leverages its nearly 100% renewable electricity mix (hydroelectric 88%, wind 10%) to electrify heating: 75% of Norwegian households heat with heat pumps or electric resistance powered by hydroelectricity, with building operational emissions close to zero.

France implemented since 2022 the RE2020 regulation that limits embodied carbon emissions in new buildings to 640 kgCO2e/m2 for housing, with progressive reduction to 415 kgCO2e/m2 by 2031, making it the first major European country to quantitatively regulate embodied carbon in construction. The Netherlands leads the circular economy in building with the Madaster platform (12,000 buildings with materials passports), the requirement for energy-positive buildings since 2021 (BENG), and a CDW landfill tax of 33 EUR/tonne that drives recycling rates of 95%. Outside Europe, Singapore stands out with its Green Mark program certifying 49% of the built stock, and its Building and Construction Authority requiring a 50% energy reduction in new commercial buildings from 2030 compared to 2005 (BCA, 2023). Costa Rica, with a 98% renewable electricity mix, has achieved per capita building emissions of only 0.3 tCO2/inhabitant, demonstrating that sector decarbonization is possible even in middle-income economies.

The gaps between leaders and laggards are enormous. The 10 countries with the highest per capita building emissions (led by Saudi Arabia, Kuwait, Qatar, the United States, and Australia) emit between 4 and 8 tCO2/inhabitant per year from building operations, while the 10 most efficient countries (led by Sweden, Norway, Switzerland, France, and Denmark) range from 0.3 to 1.2 tCO2/inhabitant: a factor of 5 to 20 times. Contradictions abound: the United Arab Emirates hosted COP28 in December 2023, but its per capita emissions of 20.3 tCO2 declined by only 3% between 2015 and 2023. Germany, a climate policy reference, failed its building sector target in 2022 for the third consecutive time, with emissions of 112 million tCO2 against a ceiling of 108 million (UBA, 2023). China built 2.2 billion m2 of new floor area in 2023, consuming more concrete and steel (and embodied emissions) than the entire EU in a decade.

The path toward convergence requires differentiated strategies by context. High per capita emission and high-income countries (the Persian Gulf, North America, Australia) need massive retrofitting of the existing stock, heating electrification, and strict embodied carbon regulation. Middle-income countries undergoing rapid urbanization (China, India, Brazil, Indonesia, which will add 2.2 billion new urban residents by 2050) must apply NZEB standards now to avoid locking in 40-60 years of emissions in low-quality buildings. Least developed countries, responsible for barely 4% of global emissions, need access to climate financing to build with energy efficiency from the start, avoiding the inefficiency trap that cost Europe 275 billion EUR per year in retrofitting. UNEP's Global Buildings Climate Tracker shows that the global building sector is not on a trajectory compatible with the 1.5 degrees C target: operational emissions should fall by 50% before 2030, but have declined by only 3% since 2015.