For the mechanism of global warming, the IPCC report emphasizes the impact of human activities and the correlation between the CO2 concentration and temperature increase. However, the Earth is a complex dynamic system with various factors affecting each other; great uncertainties exist regarding causes and effects of the climate changes.
Global warming, human-induced carbon emissions, and their uncertainties
FANG JingYun 1,2*, ZHU JiangLing 1,2, WANG ShaoPeng 1. YUE Chao 1 & SHEN HaiHua 1
1 Department of Ecology, Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China;
2 Climate Change Research Center, Academic Divisions of the Chinese Academy of Sciences at Peking University, Beijing 100871, China
*Corresponding author (email: firstname.lastname@example.org)
Abstract: In recent decades, there have been a number of debates on climate warming and its driving forces. Based on an extensive literature review, we suggest that (1) climate warming occurs with great uncertainty in the magnitude of the temperature increase; (2) both human activities and natural forces contribute to climate change, but their relative contributions are difficult to quantify; and (3) the dominant role of the increase in the atmospheric concentration of greenhouse gases (including CO2) in the global warming claimed by the Intergovernmental Panel on Climate Change (IPCC) is questioned by the scientific communities because of large uncertainties in the mechanisms of natural factors and anthropogenic activities and in the sources of the increased atmospheric CO2 concentration. More efforts should be made in order to clarify these uncertainties.
Global climate change, characterized mainly by global warming, is one of the biggest challenges to human society in the 21st century. Carbon emissions from fossil fuel combustion and land use change are considered the main factors causing global warming [1, 2]. Because carbon emissions affect social and economic development [3–5], climate change has been shifted from an academic topic to an international political, economic, and diplomatic issue.
The Intergovernmental Panel on Climate Change (IPCC) was jointly established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988 to evaluate climate changes and their effects on natural and social systems as well as the possible strategies that may be taken by humanity for the adaptation and mitigation of certain issues. The IPCC has published its assessment report every 5 to 7 years since it published its first report in 1990. Up to now, four assessment reports have been published by the IPCC. In 2007, the fourth assessment report (AR4) was finalized by more than 450 lead authors and over 800 contributing authors from more than 130 countries. The report is considered to reflect the current collective knowledge on the climate system, its evolution, and its anticipated future development .
The key points of AR4 are summarized as follows : (1) The global average temperature has risen by 0.74°C (0.56–0.92°C) in the past century. The rates of temperature increase on terrestrial surfaces are higher than those on oceanic surfaces and increased towards high latitudes in the Northern Hemisphere.
(2) A global average temperature increase is likely because of the increase of greenhouse gas concentrations resulting from human activities such as fossil fuel combustions and deforestation.
(3) The significant global temperature increase will cause a series of negative effects on natural systems, including snow and ice melt, sea-level rising, and disturbances in the hydrological cycle; and meanwhile the increase in CO2 concentrations will lead to the acidification of sea water. Such effects will directly or indirectly threaten terrestrial and marine ecosystems and social systems.
(4) Climate model projections indicate that global surface temperatures are likely to keep increasing by 0.2°C each 10-year in the next two decades. Even if the levels of all greenhouse gas concentrations are stabilized at the levels observed in the year 2000, the global temperature will continue to increase by 0.1°C every 10-year. Global warming will cause further feedbacks by diminishing the absorption capacity of atmospheric CO2 by land and ocean systems, thereby increasing the proportion of anthropogenic CO2 emissions that reside in the atmosphere.
For the mechanism of global warming, the IPCC report emphasizes the impact of human activities and the correlation between the CO2 concentration and temperature increase. However, the Earth is a complex dynamic system with various factors affecting each other; great uncertainties exist regarding causes and effects of the climate changes .
Therefore, the claims of the IPCC AR4 have been largely questioned. The Non-governmental International Panel on Climate Change (NIPCC), established in 2007, has introduced a number of controversial and divisive debates [8, 9]. The “Climate-gate” and “Glacier-gate” scandals have especially questioned the public credibility of the report [10, 11].
The IPCC report is no longer the most authoritative document on climate changes, as it is restricted by its political tendencies and some errors and flaws. In response to the sustained criticism and heightened public scrutiny of the IPCC AR4, the United Nations and the IPCC entrusted the InterAcademy Council (IAC) to assemble a committee to independently review the processes and procedures of the IPCC reports. The results of the review indicated that despite the great contributions and successes of the IPCC in general, its fundamental management structure should be reformed and the QA/QC monitoring procedures should be strengthened to process and assess the complex data regarding climate change .
At present, the major debates on the claims of the IPCC AR4 have focused on the following four aspects: (1) whether global warming is happening; (2) what are the main driving forces of climate change (i.e. the contribution of human activities and natural processes); (3) whether the future climate change projections based on the existing climate models are accurate; and (4) how about the degree of climate change impact is. Among these debates, the most essential one is whether global warming is caused by human activities or natural processes, which is the fundamental base for the international communities to address climate change and for the negotiation-related carbon emission reduction.
Therefore, correctly understanding climate change issues and clarifying the focus of debates are the foundation to formulating climate change policies and adapting to and mitigating climate change. We review the occurrence of global warming and its major driving force and discuss the global carbon budget related issues because of their great concern to modern society.