BREAKING THE 400 ppm BARRIER: PHYSICAL AND SOCIAL IMPLICATIONS OF THE RECENT CO2 RISE

The document analyzes the rise of atmospheric CO2, which reached a record high of over 400 ppm in May 2013, and discusses the resulting climate impacts and the necessity of immediate mitigation to avoid dangerous warming.

• Atmospheric CO2 concentrations have increased by more than 40% since 1750, rising from 278 ppm to a global average of 394 ppm in 2012. This increase is primarily driven by fossil fuel emissions, which account for two-thirds of the 545 GtC cumulative emissions, and secondarily by land use change, mainly deforestation.
• In May 2013, the Mauna Loa Observatory in Hawaii recorded a daily CO2 concentration exceeding 400 ppm for the first time in recorded history. This level is the highest in the last 800,000 years and likely the last 2.1 million years.
• The oceans have absorbed approximately 30% of anthropogenic CO2 emissions, leading to ocean acidification. This process threatens marine calcifying organisms and ecosystem services, including fisheries and coastal infrastructure; for example, reef-building corals are estimated to be lost at a rate of 1–2% per year.
• Paleoclimate records from ice cores show a strong quantitative correlation between CO2 and global surface temperature over millennial scales. While some warming events are triggered by orbital variations, CO2 acts as a decisive driver or amplifier of warming.
• Under a 'business as usual' scenario, CO2 concentrations could exceed 500 ppm by the mid-21st century, likely causing a global mean surface temperature increase of more than 2°C. Conversely, reducing emissions by 2% per year starting by 2020 could limit concentrations to below 450 ppm.
• The 400 ppm threshold is viewed as a significant political marker rather than a physical tipping point, highlighting the 'inaction and indifference' of governments toward climate changes that disproportionately affect vulnerable populations with low adaptive capacity.

APA

Faria, S. H., Spadaro, J. V., & Markandya, A. (2013). BREAKING THE 400 ppm BARRIER: PHYSICAL AND SOCIAL IMPLICATIONS OF THE RECENT CO2 RISE. Basque Centre for Climate Change. https://www.bc3research.org/h6T8Uy8Nm4gFs0O/201401130413341104337663.pdf

Chicago

Faria, Sérgio H., Joseph V. Spadaro, and Anil Markandya. BREAKING THE 400 ppm BARRIER: PHYSICAL AND SOCIAL IMPLICATIONS OF THE RECENT CO2 RISE. Basque Centre for Climate Change, 2013. https://www.bc3research.org/h6T8Uy8Nm4gFs0O/201401130413341104337663.pdf.

Wikipedia

{{cite report |last1=Faria |first1=Sérgio H. |last2=Spadaro |first2=Joseph V. |last3=Markandya |first3=Anil |title=BREAKING THE 400 ppm BARRIER: PHYSICAL AND SOCIAL IMPLICATIONS OF THE RECENT CO2 RISE |publisher=Basque Centre for Climate Change |date=2013 |url=https://www.bc3research.org/h6T8Uy8Nm4gFs0O/201401130413341104337663.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{faria2013breaking, author = {Faria, Sérgio H. and Spadaro, Joseph V. and Markandya, Anil}, title = {{BREAKING THE 400 ppm BARRIER: PHYSICAL AND SOCIAL IMPLICATIONS OF THE RECENT CO2 RISE}}, institution = {Basque Centre for Climate Change}, year = {2013}, url = {https://www.bc3research.org/h6T8Uy8Nm4gFs0O/201401130413341104337663.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }