With the extensive use of fossil fuels, deforestation, and land-use change, anthropogenic activities have contributed to the ever-increasing concentrations of greenhouse gases (GHGs) in the atmosphere, causing global climate change. In response to the worsening global climate change, achieving carbon (C) neutrality by the middle century is the most pressing task on the planet. What are the paths to C neutralization? What are the directions for technological breakthroughs to achieve C neutralization? How to monitor and measure C emissions? This review, prepared by 58 scientists from 8 countries and 52 research units, intends to provide insights into the innovative technologies that offer solutions achieving C neutrality and sustainable development.
Achieving C neutrality requires replacing fossil fuels with renewable energy sources. Harnessing the power of solar, wind, geothermal, ocean, nuclear, and H2 energy may help secure global energy security without relying on fossil fuels. Bioenergy is also important in reshaping the energy supply and consumption systems. Technologies for these renewable energy sources and their future development are discussed (Fig. 2).
Fig. 2 Technologies for renewable energy
Technologies for enhancing C sink in global ecosystems
Global agricultural food systems are the major source of global anthropogenic GHG emissions, while terrestrial and marine ecosystems are the most important global C sinks (Fig. 3). To avoid disastrous climate change, global ecosystems need to be reformed to increase C sequestration, biomass production, and food supply while lowering GHG emissions.
Fig. 3 Overview of global GHG budget and strategies to promote GHG reduction and sequestration in global ecosystems
As an effective strategy to reduce the C footprint of global waste, thermochemical conversion of solid waste into biochar can bring multifunctional benefits to the circular economy in addition to climate change mitigation and C sequestration. A plethora of organic resources, such as crop residues, forest residues, livestock manure, food wastes, industrial biowastes, municipal biowastes, animal carcasses, are feedstocks that can be used to produce biochar for different purposes. Biochar is used in a variety of applications, including soil amendment, delivery of agrochemicals and microbes, environmental remediation, catalyst production, building material manufacturing, and feed formulation (Fig. 4).
Fig. 4 Zero waste biochar as a C-neutral tool for sustainable development
Technologies for C capture, utilization, and storage
CCUS, technologies for carbon capture, utilization, and storage, are critical to achieving C neutrality (Fig. 5). CCUS technologies need innovations, targeting CO2 recovery with low energy or even zero energy penalty, and aiming collaborative optimization of CO2 storage and resource recovery and risk management. Chemicals-power polygeneration and chemical looping combustion with CO2 capture have the potentials to realize low-cost CO2 capture. Fossil fuels combined with renewable energy for CO2capture, the complementary energy systems, may play an important role for future CCUS. The conversion of CO2 into fuels and chemicals is a promising direction for C reduction.
Fig. 5 The roadmap for CO2 capture technology development in the industry
C neutrality based on satellite observations and digital earth
Satellite observation and digital earth technology are important parts of monitoring C emissions and establishing an air-space-ground integrated observation system for the C cycle. They can provide basic observation and analysis data with a high temporal and spatial resolution for C neutralization research. C satellite and multispectral satellites can provide data support for monitoring the concentration of greenhouse gases; digital earth technology can integrate global vegetation, atmosphere, and climate data to provide temporal and spatial analysis of the C budget of natural ecosystems.
As the world races towards C neutrality, it is critical to revise current global C fluxes. To meet the climate change mitigation goals by the middle century, all people including investors, researchers, policy makers and consumers must work together:
(1) To realize orderly reduction and replacement of fossil fuel energy sources with renewable energy sources, we need to vigorously develop energy storage systems to address the intermittency of renewable energy sources. (2) To coordinate ecosystem protection and carbon sequestration, we need to push forward reform of crop-livestock production systems based on land use and improving ecological carbon sink. (3) To integrate ecological strategies optimizing biochar production, life cycle analysis, and formulate standards to advance the development of green and low-carbon industries. (4) To adopt breakthrough CCUS technologies including polygeneration, chemical looping combustion, and fossil fuels combined with renewable energy for CO2 capture, to overcome the high energy consumption and high costs. (5) To develop new satellites to comprehensively and timely monitor GHG emissions, and to expand the ability to calculate C budgets through joint observation from space and the ground.