Satellite CO₂ retrievals from the Greenhouse gases Observing SATellite (GOSAT), Atmospheric Infrared Sounder (AIRS), and Tropospheric Emission Spectrometer (TES) and in situ measurements from the National Oceanic and Atmospheric Administration ‐ Earth System Research Laboratory (NOAA‐ESRL) Surface CO₂ and Total Carbon Column Observing Network (TCCON) are utilized to explore the CO₂ variability at different altitudes. A multiple regression method is used to calculate the CO₂ annual cycle and semiannual cycle amplitudes from different data sets. The CO₂ annual cycle and semiannual cycle amplitudes for GOSAT X_CO2 and TCCON X_CO2 are consistent but smaller than those seen in the NOAA‐ESRL surface data. The CO₂ annual and semiannual cycles are smallest in the AIRS midtropospheric CO₂ compared with other data sets in the Northern Hemisphere. The amplitudes for the CO₂ annual cycle and semiannual cycle from GOSAT, TES, and AIRS CO₂ are small and comparable to each other in the Southern Hemisphere. Similar regression analysis is applied to the Model for OZone And Related chemical Tracers‐2 and CarbonTracker model CO₂. The convolved model CO₂ annual cycle and semiannual cycle amplitudes are similar to those from the satellite CO₂ retrievals, although the models tend to underestimate the CO₂ seasonal cycle amplitudes in the Northern Hemisphere midlatitudes and underestimate the CO₂ semiannual cycle amplitudes in the high latitudes. These results can be used to better understand the vertical structures for the CO₂ annual cycle and semiannual cycle and help identify deficiencies in the models, which are very important for the carbon budget study.

We show that the reconstructed sensitivity of the sea level temperature to long term solar forcing in the Northern Hemisphere is in very good agreement with the empirical temperature pattern corresponding to changes of the North Annular Mode (NAM). This implies that long‐term variations of solar output affect climate predominantly through the NAM that extends throughout the stratosphere and troposphere.

The Congo basin, with an area of about 3.7 million km² in the tropical region, contains the second largest rainforest and is considered as a carbon sink for the atmosphere. Here, using Orbiting Carbon Observatory‐2 satellite observations, we show that the atmospheric CO₂ over the Congo basin is ∼2 ppm higher than the regional background during June–August, which is primarily due to biomass burning and significantly reduced photosynthetic activities during the dry season. The contribution from the biomass burning is larger than that from the biosphere during June–August. Current budget estimations suggest emissions from biomass burning during the dry season alone account for ∼72% of the Congo basin annual biomass burning emissions and are ∼40% more than the largest terrestrial uptake in the same region during January–March (wet season). Therefore, better seasonal fire management in this region is an important strategy for achieving timely reductions in global carbon emissions as set by international agreements.

Previous studies suggested that the Amazon, the largest rainforest on Earth, changes from a CO₂ sink to a CO₂ source during the dry/fire season. However, the biospheric contributions to atmospheric CO₂ are not well understood during the two main seasons, the dry/fire season and the wet season. In this article, we utilize Orbiting Carbon Observatory 2 (OCO‐2) Solar‐Induced Fluorescence (SIF) to explore photosynthetic activity during the different seasons. The spatiotemporal variability of OCO‐2 SIF, OCO‐2 CO₂, precipitation, and burned area are investigated over the Amazon from September 2014 to December 2019. Averaging over the entire Amazon region, we found a positive temporal correlation (0.94) between OCO‐2 SIF and Global Precipitation Climatology Project precipitation and a negative temporal correlation (−0.64) between OCO‐2 SIF and OCO‐2 CO₂, consistent with the fact that precipitation enhances photosynthesis, which results in higher values for SIF and rate of removal of CO₂ from the atmosphere above the Amazon region. We also observed seasonality in the spatial variability of these variables within the Amazon region. During the dry/fire (August–October) season, low SIF values, low precipitation, high vapor pressure deficit (VPD), large burned areas, and high atmospheric CO₂ are mainly found over the southern Amazon region. In contrast, during the wet season (January–March), high SIF values, high precipitation, low VPD, smaller burned areas, and low CO₂ are found over both the central and southern Amazon regions. The seasonal difference in SIF suggests that photosynthetic activity is reduced during the dry/fire season relative to the wet season as a result of low precipitation and high VPD, especially over the southern Amazon region, which will contribute to more CO₂ in the atmosphere during the dry/fire season.

Advanced satellite technology has been providing unique observations of global carbon dioxide (CO₂) concentrations. These observations have revealed important CO₂ variability at different timescales and over regional and planetary scales. Satellite CO₂ retrievals have revealed that stratospheric sudden warming and the Madden-Julian Oscillation can modulate atmospheric CO₂ concentrations in the mid-troposphere. Atmospheric CO₂ also demonstrates variability at interannual timescales. In the tropical region, the El Niño–Southern Oscillation and the Tropospheric Biennial Oscillation can change atmospheric CO₂ concentrations. At high latitudes, mid-tropospheric CO₂ concentrations can be influenced by the Northern Hemispheric annular mode. In addition to modulations by the large-scale circulations, sporadic events such as wildfires, volcanic eruptions, and droughts, which change CO₂ surface emissions, can cause atmospheric CO₂ concentrations to increase significantly. The natural variability of CO₂ summarized in this review can help us better understand its sources and sinks and its redistribution by atmospheric motion. ▪ Global satellite CO₂ data offer a unique opportunity to explore CO₂ variability in different regions. ▪ Atmospheric CO₂ concentration demonstrates variations at intraseasonal, seasonal, and interannual timescales. ▪ Both large-scale circulations and variations of surface emissions can modulate CO₂ concentrations in the atmosphere.