Fossil fuels are also called carbonaceous fuels because they are high in carbon compounds.

The Intergovernmental Panel on Climate Change (IPCC), an international body for assessing the science related to climate change, released a Special Report on Global Warming of 1.5°C (about 2.7°F) in October 2018. The report specifically addressed the need for carbon capture and storage to remove carbon dioxide from the atmosphere, but noted that this required a major investment in developing this technology. Please find more information about the reports finding here: http://report.ipcc.ch/sr15/pdf/sr15_spm_final.pdf and a news article about the report here: https://www.sciencedaily.com/releases/2018/10/181008075147.htm and many opinions: https://www.brookings.edu/opinions/were-almost-out-of-time-the-alarming-ipcc-climate-report-and-what-to-do-next/

Part per million (ppm) is a unit of concentration commonly used in atmospheric science and is equivalent to 10\(^{-6}\).

Cloud condensation nuclei (CCN) are small particle that facilitate cloud growth by serving as location of water vapor condensation in the atmosphere. Aerosols often act as surfaced for cloud droplet growth.

The \(\delta\) is a Greek symbol used to represent instantaneous change. Here, the authors are providing a numerical value of the change of aerosol optical depth in the Southern Hemisphere (SH), compared to natural background.

Particles, or aerosols, in the atmosphere, such as dust or smoke, scatter or absorb sunlight. Aerosol optical depth (AOD) tells us how much sunlight was prevented from reaching the surface due to these particles. It is a unitless values that corresponds to the amount of aerosols in the atmosphere over the location where is was measured, often using a satellite.

The stratosphere is the layer of the atmosphere above the troposphere, extending 32 miles above the Earth's surface. The stratosphere is relatively stable compared to the troposphere and gets its name from the stratification of temperature. The lower sections of the Stratosphere is colder, while the higher parts of this layer are warmer due to the occurrence of the ozone layer. Commercial flights often fly at the lower ends of the stratosphere because the conditions improve fuel efficiency and reduce interruptions from weather events in the troposphere.

Sulfate aerosols are formed from the condensation of oxidized sulfur dioxide (SO\(_2\)) emitted from fossil fuels combustion or volcanoes. Because humans are the main source of sulfate aerosols, the concentration of this particle is higher over land in the Northern Hemisphere, which the majority of industrial processes take place. The remainder of this paper provides more details on the different impacts these aerosols have on the Earth system.

Planetary albedo is a measurement of the amount of light reflected from the surface of a planet, in this case, the Earth. Aerosols that reflect more light, such as sulfate aerosols, will enhance the planetary albedo so more incoming solar radiation is reflected back to space. Scientists estimate that Earth's average albedo is 0.3.

Relative humidity (RH) is the ratio of the amount of water vapor in the air (actual vapor density) relative to the amount of water the air could hold (saturation vapor density)

It is given by: \(Relative Humidity\) = \((\dfrac{actual vapor density}{saturation vapor density})\)\(*100%\)

The relative humidity is simply a way for meteorologists and scientists to describe how much moisture is in the air at a give temperature. You and I might feel this on a warm day, where is feels much hotter outside when the humidity is higher.

Hygroscopic means that the particle has the tendency to absorb water or to react with water.

Flux means a change in, so in this case, the authors are referring to a change (in and out) of the global mean top-of-the-atmosphere radiative forcing.

In this case, deliquescent means that the particles absorb moisture.

Measurements of temperature or other weather conditions, such as relative humidity, are called in situ if they are taken in the original location. It is a latin phrase used to differentiate observations taken from satellites, called remote observations.

A mole is an SI unit for the amount of a substance or chemical.

Meteorology is the study of weather, so meteorlogical processes refer to weather events such a winds or thunderstorms.

Longitudes are the imaginary North-South lines drawn on planet Earth so navigators, scientists, and other can establish precise locations.

Some sulfate compounds come from naturally occurring, or biogenic sources, such as dimethylsulfide (DMS) produced from ocean bacteria.

Climate models are numerical representations of the Earth system. Some models are very complex and can take months to run on a supercomputer, others can be run on a laptop in a matter of seconds. More complex models include representations of the atmosphere, oceans, and change in ice dynamics. Simple climate models often represent on the most fundamental physics of the climate system, such as a carbon cycle.

Greenhouse gases (GHGs) absorb outgoing infrared radiation and trap the energy in the atmosphere, causing an increase in temperature over time called greenhouse warming.

Greenhouse gases (GHGs) are atmospheric species that absorb outgoing infrared radiation, such as carbon dioxide (CO\(_2\)) and chlorofluerocarbons (HFCs). GHG have long atmospheric lifetimes ranging from hundreds to thousands of year depending on their chemical and radiative properties. These differences also impacts their radiative forcing abilities.

The troposphere is the area of the atmosphere where you and I live and breathe. It is between 5 - 9 miles thick, depending on your location on Earth. Its name derives from "Tropos”, meaning change, because weather and clouds form in this region of the atmosphere.

Aerosols are small particles suspended in the atmosphere. Sunlight can be absorbed or reflected from the surface of aerosols depending on the size and type of aerosols. These factor determine the atmospheric properties of the aerosol. Aerosols generally have short atmospheric lifetimes compared to greenhouse gases, such as carbon dioxide. For example, black carbon, a type of aerosol emitted from incomplete combustion and biomass burning, have an atmospheric lifetime between 3-5 days.

Tropospheric aerosols are very important to understand because they impact the climate, but also can impact the quality of human health. For example, very fine particles, called Particulate Matter (PM) 2.5, a reference to the diameter of the aerosols in micrometers, are dangerous from humans and leads to increased cardiovascular problems and even death.

Climate scientists generally use the Industrial Revolution as a benchmark in time. Though there is debate in some spheres about the exact date that should be chose, these authors use 1850 to indicate the shift toward industrialization, including use of fossil fuels. Time periods before 1850 are termed "pre-industrial."

The Earth's surface temperature is determined by the balance between incoming solar radiation (sunlight) and outgoing infrared radiation. Radiative forcing (RF) is a measure of the ability of a gas or particle, for example, to effect that energy balance. The units of RF are watt per meter squared (W/m\(^2\)), which translate to the rate of energy change per unit area on the globe as measured from the top of the atmosphere.

Climate change refers to changes in the Earth system from both natural and human factors. Global warming is often use synonymously with climate change, but global warming specifically refers to the rise in global average temperature. More generally, climate change includes the melting of polar ice, increase in ocean acidity, and measured global mean temperature increases.

Anthropogenic means resulting from human activity. Scientists often speak about anthropogenic climate change to specifically discuss the changes resulting from the burning of fossil fuels or land use change, for example.

In this context, marginal means not important or not central.