Climate Change Science

The Greenhouse Gas Effect & Climate Change

Earth’s climate is largely driven by energy that comes from the sun. When solar radiation reaches the Earth’s atmosphere, some of it is reflected into space and a portion is absorbed by the Earth’s surface. As the Earth absorbs solar radiation, its surface heats up and re-radiates heat back out into the atmosphere.  While some of the heat escapes past the atmosphere into space, gases in the atmosphere prevent the loss of some of the heat. The gases trapping the heat are known as greenhouse gases (GHG). Without some GHGs in the atmosphere, the Earth would not be warm enough to sustain life as we know it. This heat trapping quality of gases in Earth’s atmosphere is known as the greenhouse effect. Increased levels of specific GHGs in the atmosphere means that less heat escapes to space. More heat trapped in the atmosphere leads to much hotter than average temperatures also known as global warming, which in turn contributes to more intense storms, drought, extreme heat events, and sea level rise. These effects are considered climate change.

Human-caused climate change is well understood and widely accepted by the scientific community, with over 97 percent of climate scientists agreeing that the planet is warming and human activities are the root cause. Human activities have raised the levels of GHGs in the atmosphere from 280 parts per million to over 410 parts per million in the last 150 years. Although many changes to climate are governed by natural processes, human activities have added GHGs to the atmosphere at a rate that is unprecedented in Earth’s history, leading to CO2 levels that are now higher than they have been any time in the past 800,000 years.

Globally, climate change is already impacting both human and natural systems. Scientists have measured shrinking ice sheets, warming, and acidifying oceans, increasing global temperatures, less snow cover, sea level rise, and species extinction. The potential consequences of these climate change related impacts include the flooding of low-lying areas, reduction of fresh-water supply, adverse changes to biological resources and public health, as well as many other adverse environmental consequences.

Greenhouse Gas Effect

Since the advent of the industrial revolution human activities such as burning fossil fuels and deforestation have caused a substantial increase in the concentration of greenhouse gases in the atmosphere.

The Result: Extra Trapped Heat & Higher Global Temperatures.

Globally, a warming trend is abundantly clear, with nineteen of the hottest years on record occurring since 2000. The year 2020 tied with 2016 for the hottest year on record since record- keeping began in 1880, and these trends are consistent across numerous monitoring agencies and data sets. NASA recorded July 2023 as the hottest month on record since 1880.

Though climate change is a global phenomenon it has the potential to impact facets of society on the local level including health outcomes, natural resource access, infrastructure, emergency response, tourism, and frequency of disasters. The United Nations Intergovernmental Panel on Climate Change (IPCC) projections show that a reduction in GHG emission to carbon neutrality by mid-century is required to limit warming trends to 1.5 degrees Celsius and avoid the worst impacts of climate change. In order to do this, action must be taken at all levels of society to reduce emissions of GHGs.

Source: Climate Central

Types of GHG Emissions

The IPCC lists the following GHGs: carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), as well as chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride, which are collectively called fluorinated gases.14 Almost all the GHGs emitted in the United States each year consist of CO2, CH4, and N2O, while fluorinated gases make up the remaining emissions15 . Because CO2, CH4, and N2O comprise a large majority of GHG emissions at the community level, these are the gases considered in this analysis.

Each GHG has a different propensity for trapping heat in the atmosphere, known as its global warming potential (GWP). GHGs also last for different periods of time in the atmosphere, ranging from a decade to several thousand years. Because all the GHGs have different characteristics, a standard unit is needed to compare the potential impact of different GHGs and allow them to be added up in an analysis. This is achieved by converting all GHGs into the standard unit known as a carbon dioxide equivalent (CO2e), based on the amount of heat one metric ton (MT) of CO2 traps in the atmosphere. GWP for each GHG was drawn from the IPCC fifth Assessment Report16 , which represents the best available scientific consensus and is consistent with the methodology outlined in the California Air Resources Board (CARB) Scoping Plan. Since CO2 is used as the reference point for trapping heat, CO2 has a GWP of 1. Methane has a GWP of 28, meaning that each metric ton (MT) of methane causes 28 times more warming than 1 MT of CO2. Nitrous oxide has a GWP of 265, meaning 265 times the GWP of 1 MT of CO2. 17

Sources of GHG Emissions

The combustion of fossil fuels is the primary source of GHG emissions, decomposition of waste, and land use change are also major contributors. It can be helpful to understand how different sectors contribute to total emissions. The top sources of GHGs Statewide are transportation (37 percent), industrial processes (20 percent), and electric power (16 percent). The magnitude of total California GHG emissions is due in part to its large size and large population compared to other states. However, a factor that reduces California per capita fuel use and GHG emissions as compared to other states is its relatively mild climate. 18

The main sources of GHG emissions in Hayward are from transportation, buildings, and waste. Transportation emissions are generated by fuels used to power cars, trucks, public transit, and off- road vehicles. Building emissions are associated with electricity and natural gas used by commercial, residential, and municipal buildings. Waste from residential, commercial, and municipal sources generates methane emissions as material (especially organics like food scraps and yard waste) decomposes in the landfill.

Opportunities to Reduce GHG Emissions

Cities play a crucial role in reducing GHG emissions in California. The policies and initiatives implemented by local governments have the capability to influence activities that can affect high- emissions behaviors, mitigate the consequences of climate change, and equip the community to better withstand its effects. Cities hold the potential to drive climate action and emission reduction through strategic land use planning, the revision of building codes and standards, and developing partnerships between public and private entities that promote shifts in behavior. They can enact various measures to decrease emissions, including enhancing building regulations to curtail energy consumption, offering incentives for alternative transportation methods to reduce fuel usage, broadening options for diverting waste and utilizing renewable energy sources, as well as educating residents about their roles as both citizens and consumers.

Climate Change Impacts

Climate change already has impacted and will continue to impact the Hayward community, including its residents, businesses, and visitors. In the past few years, Hayward has experienced severe droughts, poor air quality from regional wildfire smoke, local flooding from extreme precipitation events, extreme heat events, and rising sea levels. As the climate continues to change, many climate hazards may become more frequent and intense. In 2016, the California legislature adopted Senate Bill (SB) 1000 requiring local jurisdictions to review and update Safety Elements of the General Plan to address and update hazards related to flooding, fires and to include climate adaptation and resilience strategies. The Hayward General Plan includes a Hazards Element that addresses State requirements for a Safety Element. As such, in support of the update to the Hayward General Plan Hazards Element, the City prepared a climate change vulnerability assessment to evaluate the potential impacts of climate change on community assets and populations. The climate change vulnerability assessment describes the community’s vulnerabilities to climate change and provides a foundation to develop strategies to increase community resilience. A summary of climate exposures and potential impacts within Hayward as identified in the Hayward Hazards Element is summarized in Figure 1.

Figure 1: Hayward Climate Change Exposure & Impacts