The UN has stated that global carbon neutrality should be reached by the second half of the century if the total global temperature rise is to be limited to 2 degrees Celsius (about 3.6 degrees Fahrenheit).

Accomplishing this would keep maximum amount of carbon dioxide (CO2) that can be emitted into the atmosphere while keeping the global temperature at a safe level after the year 2020, the UN Environment Programme (UNEP).  The statement was based off UNEP's Emissions Gap Report 2014, which looks at what countries are on track to meet global climate goals.

If the global carbon budget of 1,000 gigatonnes is exceeded, it could significantly increase the risk of severe and possibly permanent climate change impacts. The report found many countries are getting more serious about where they need to be in terms of total emissions by the years 2025 and 2030. The report outlines a "peaking of emissions within the next ten years, a halving of all greenhouse gas emissions by mid-century; and in the second half of the century, carbon neutrality followed by net zero total greenhouse gas emissions."

"The Sustainable Development Goals underscore the many synergies between development and climate change mitigation goals. Linking development policies with climate mitigation will help countries build the energy-efficient, low-carbon infrastructures of the future and achieve transformational change that echoes the true meaning of sustainable development," said Achim Steiner, UN Under-Secretary-General and Executive Director of UNEP.

To avoid exceeding this crucial budget and keeping global temperature rise below 2 degrees carbon neutrality (meaning total CO2 emissions hitting net zero on the global scale). Net zero implies some CO2 emissions remain, but is compensated by the same amount of carbon dioxide uptake or "negative emissions."  When taking non-CO2 gases such as methane, nitrous oxide and hydrofluorocarbons. Total global greenhouse gas emissions are expected to reach net zero by between 2080 and 2100.