22 September 2019: A synthesis report titled, ‘United in Science,’ marshals the growing evidence that “climate impacts are hitting harder and sooner than climate assessments indicated even a decade ago,” with a real risk of crossing critical tipping points. Coordinated by the World Meteorological Organization (WMO) the report was commissioned by the Science Advisory Group to the UN Secretary-General’s Climate Action Summit with a view to providing a “transparent envelope” of authoritative and actionable cutting-edge science to world leaders.

The synthesis report provides a cohesive assessment of the state of the earth system under the increasing influence of anthropogenic climate change. It also outlines humanity’s response thus far, and makes projections of the far-reaching changes of the global climate in the future. The report is structured around key messages as well as short summaries of global studies conducted by the contributing agencies.

Data sources used in the report include the WMO Global Atmosphere Watch, the UN Environment Programme (UNEP) Emissions Gap Report, three IPCC Special Reports released in 2018 and 2019 (the Special Report on Global Warming of 1.5°C (SR15), the Special Report on Climate Change and Land (SRCCL) and the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC)), as well as studies by the Global Carbon Project, Future Earth and Earth League, and the Global Framework for Climate Services.

Some of the conclusions highlighted in the synthesis include:

• Global average temperature for 2015-2019 is on track to be the warmest of any equivalent period on record. It has already increased by 1.1°C above preindustrial levels, and it is now 0.2°C warmer than 2011-2015.
• Levels of the main long-lived greenhouse gases (GHGs), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) have reached new highs, locking in the warming trend for generations to come.
• The emissions gap in 2030 between emission levels under full implementation of conditional Nationally Determined Contributions (NDCs) and levels consistent with least-cost pathways to the 2°C target is 13 gigatons of CO2 equivalent (GtCO2e). If just the unconditional NDCs are implemented, the gap increases to 15 GtCO2e. The gap in the case of the 1.5°C target is 29 GtCO2e and 32 GtCO2e, respectively.
• The level of ambition in current NDCs needs to be roughly tripled to align with the 2°C limit and increased around fivefold to align with the 1.5°C limit.

The report emphasizes that the Paris Agreement on climate change can only be achieved if “immediate and all-inclusive action” is taken, encompassing deep decarbonization, complemented by ambitious policy measures, protection and enhancement of carbon sinks and biodiversity, and efforts to remove CO2 from the atmosphere. With regard to bridging the emissions gap, the report adds that part of the technical potential can be realized through scaling up and replicating existing, well-proven policies that simultaneously contribute to key SDGs such as switching to renewable energy and reforestation. [Publication: United in Science] [UN Press Release] [UNFCCC Press Release] [WMO Press Release on Report] [WMO Press Release on Background Study] [UNEP Press Release] [UN News Story] [WMO Webpage of Science Advisory Group]