Human Impact on the Environment

Question 1

draw the carbon cycle (there are 11 arrows)

Answer 1

ans on page 2 in booklet

Question 2

describe the effect of deforestation on the carbon cycle in 4 points

Answer 2

increases CO2 content in atmosphere:
removal of trees means less uptake of CO2 from atmosphere due to less photosynthesis

plants store carbon as biomass so burning woody parts of trees releases cO2 into atmosphere

forested replaced by crops which store less CO2 and when crops die, decomposers undertake decay, releasing CO2

forest often replaced with cattle that produce high levels of CO2 and greenhouse gases e.g. methane

Question 3

describe the cause of climate change in three points - not specific

Answer 3

human activities have resulted in global and regional climate patterns changing noticeably in second half of 20th century

cause thought to be the huge rise in atmospheric CO2 levels and rise in other greenhouse gases e.g. CO2, methane, nitrous oxides and water vapour

two main reasons for rise in CO2 are combustion; burning of fossil fuels releases CO2 that was previously locked up, and deforestation

Question 4

describe the effect of global warming in five points

Answer 4

CO2 is an important greenhouse gas, as it absorbs radiation from Earth

if it (radiation) accumulates in excess, it leads to global warming

this has resulted in increased frequency of extreme weather conditions, polar ice caps melting and increased number of forest fires

therefore, species distribution may change; plants and animals may be driven to extinction if cannot find a suitable new habitat fast enough, reducing biodiversity

in some regions, there may be increased crop yields, but pest populations may also increase

Question 5

describe the effect of ocean warming

Answer 5

oceans can store a lot of heat so there is a time lag between warming of the atmosphere (which is linked to global atmosphere CO2 levels) and the warming of the ocean

CO2 is acidic in solution/CO2 dissolves in oceans making them more acidic

Question 6

give 5 consequences of global warming and climate change on aquatic habitats

Answer 6

decreased pH (acidification) of oceans - corals die, damages mollusc shells

increased rates of photosynthesis in aquatic habitats causing algal blooms

less oxygen dissolved in water at higher temps

fish migrate to cooler waters

reduced productivity on fish farming industry

Question 7

describe the effect of climate change with farming practices - give 3 points

Answer 7

agriculture particularly vulnerable to impacts of climate change and is affected through changes in temperature, and timing & quantity of rain
e.g. more flooding in the UK

extreme events, e.g. droughts and floods likely to be more frequent due to climate change

as global warming increases, fresh water will be critical to sustain food production and feed growing human population

Question 8

what are some possible changes in farming practices?

Answer 8

rotating crops to reduce pests and mineral depletion

salt-tolerant crops to overcome rising sea levels

feeding cows high-sugar grasses with less cellulose to reduce the release of the greenhouse gas methane

drought-resistant crops to tackle the low and fluctuating water supply

improving drainage to aerate water-logged and anaerobic soils
re-instating meadows

keeping the soil healthy by using minimal preparation of land for growing crops (tillage) and cover crops like clover to protect and improve soils between crops

Question 9

describe the effect of tillage on soil residue

Answer 9

conventional tillage leaves less than 15% residue on the soil surface

conservation tillage leaves at least 30% residue on the soil surface

no tillage leaves the soil covered 100% of the time

Question 10

what does carbon footprint mean?

Answer 10

this is the total amount of carbon attributable to the actions of an individual, a product, or service over a period of one year

Question 11

how can we reduce our carbon footprint?

Answer 11

recycle more

eat less meat

drive less

use less heating - insulation, clothing etc

avoid food waste

plant trees

Question 12

draw the nitrogen cycle

Answer 12

page 5 and 8 in booklet

Question 13

why is nitrogen important to all living organisms?

Answer 13

to make proteins

to make ATP, DNA and RNA

nucleic acids, chlorophyll, amino acids

Question 14

by which process do plants and animals absorb ammonium or nitrate ions through their roots?

Answer 14

facilitated diffusion

active transport

Question 15

name two pathways that these ions (ammonium/nitrate) can take when travelling through the cortex cells of a plant root?

Answer 15

apoplast - through cell walls

symplast - cytoplasm, plasmodesmata

Question 16

what is ammonification?

Answer 16

decomposers (saprotrophs and detritivores) result in the decay of dead plants and animals, faeces and urine into ammonium ions

Question 17

describe nitrification

Answer 17

the ammonium ions produced by decomposers are converted into nitrites and then nitrates by nitrifying bacteria

aerobic conditions are required for this process

plants can then absorb these nitrate ions and incorporate them into amino acids, nucleotides and chlorophyll

Question 18

what are the names of two nitrifying bacteria and what do they do?

Answer 18

nitrosomonas convert ammonium ions -> nitrites

nitrobacter converts nitrites -> nitrates

Question 19

what is nitrogen fixation?

Answer 19

nitrogen fixing bacteria can directly fix nitrogen gas into ammonium ions

Question 20

what are the name of two nitrogen-fixing bacteria and their roles?

Answer 20

azotobacter are free living in the soil

rhizobium found in root nodules of leguminous plants

Question 21

describe rhizobium in detail

Answer 21

rhizobium (aerobic bacterium) are symbiotic bacteria found in root nodules of legumes, e.g. clover and pea plants

when nitrogen gas diffuses into root nodule, rhizobium produces nitrogenase (inhibited by O2) enzyme which catalyses the fixation of nitrogen gas into ammonium ions

these ammonium ions can then be converted into amino acids for use by the plant

however, nitrogenase is inhibited by oxygen

therefore, haemoglobin is present in root nodules to bind with the oxygen

the presence of haemoglobin gives them a pink colour

Question 22

why can the relationship between the bacteria in the root nodule and the legume be classed as a symbiotic mutualistic relationship?

Answer 22

bacteria: a place to live, protection, gain sugars from plant photosynthesis

plant: ammonium

Question 23

what is assimilation?

Answer 23

the formation of organic nitrogen compounds (e.g. amino acids) from inorganic nitrogen compounds present in the environment

Question 24

describe denitrification

Answer 24

denitrifying bacteria (e.g. pseudomonas) convert nitrate from the soil into nitrogen gas

this is a problem as it removes useful nitrogenous compounds from the soil

anaerobic conditions are required for this and it occurs most often in waterlogged soils

Question 25

how does ploughing and drainage of soil aid the nitrogen cycle?

Answer 25

improves aeration this enables nitrifying bacteria to convert ammonium ions into nitrate and prevents denitrifying bacteria from completing denitrification

Question 26

how does cultivation of legumes in soils lacking nitrogen aid the nitrogen cycle?

Answer 26

so that Rhizobium will carry out nitrogen fixation within the plants and then when the plants die these nitrogenous compounds will enter the soil to be broken down by decomposers in ammonification

Question 27

what is another human activity that aids the nitrogen cycle?

Answer 27

application of artificial fertilisers and manure to soil that will enable a greater yield of crop plants

Question 28

what do fertilisers contain?

Answer 28

nitrates phosphates potassium

Question 29

why do crops need fertilisers?

Answer 29

nitrates to produce amino acids (proteins), nucleic acids and ATP phosphate for phospholipids and ATP potassium for stomatal opening

Question 30

describe the process of eutrophication (6 steps)

Answer 30

fertilisers leach into watercourses, increasing levels of nutrients e.g. nitrogen there is a bloom of algae, blocking out the light to plants below these plants die as they can't photosynthesis decomposers such as bacteria and fungi decompose the dead organic matter as these bacteria respire aerobically they use most of the available oxygen this creates a biological oxygen demand (BOD) aquatic animals die due to lack of oxygen anaerobic bacteria then flourish

Question 31

how can high nitrate levels in waterways be overcome by?

Answer 31

restricting the amount of fertiliser added to soil only applying fertiliser when crops are actively growing so that it is readily taken up and does not remain in the soil digging drainage ditches for minerals to concentrate in this however has led to a drop in invertebrate biodiversity and has reduced species diversity in nearby grasslands

Question 32

define endangered species

Answer 32

they are those that are at serious risk of extinction

Question 33

define extinction

Answer 33

when there are no living members of a species left it is a natural process

Question 34

what are 9 threats to species?

Answer 34

natural selection non-contiguous populations deforestation drainage of wetlands hedgerow loss crop sowing seasons overhunting competition from other introduced species pollution

Question 35

explain natural selection as a threat to species and give an example

Answer 35

humans are changing environments faster than new mutations allow organism to adapt Javan tiger

Question 36

explain non-contiguous populations as a threat to species and give an example

Answer 36

if small populations are isolated from each other and are unable to interbreed there may not be enough genetic diversity to ensure a healthy population black rhinos in africa

Question 37

explain deforestation as a threat to species and give an example

Answer 37

permanent removal of trees removes habitats javan tiger

Question 38

explain drainage of wetlands as a threat to species and give an example

Answer 38

wetlands are drained to allow agriculture or building this destroys habitats large copper butterfly now extinct in Uk

Question 39

explain hedgerow loss as a threat to species and give an example

Answer 39

removal of hedgerows which have separated fields for centuries removes breeding sites, feeding sites and wildlife 'corridors' which allow animals to move from one area to another dormouse may face extinction in UK

Question 40

explain crop sowing seasons as a threat to species and give an example

Answer 40

sowing during autumn rather than spring means plants are unsuitable heights for birds to build nests skylark and lapwing are in decline

Question 41

explain overhunting as a threat to species and give an example

Answer 41

for trophies, traditional medicine, 'bush meat', overfishing, agricultural exploitation pyrenean ibex

Question 42

explain competition from other introduced species as a threat to species and give an example

Answer 42

domestic animals and accidentally introduced animals predate or outcompete native species dodo, red squirrels in uk

Question 43

explain pollution as a threat to species and give an example

Answer 43

pollutants kill organisms or make it difficult for them to survive in their habitat Oil spills, PCBs

Question 44

define conservation

Answer 44

is the protection, preservation, management and restoration of natural habitats and communities; enhancing biodiversity whilst still allowing human activity

Question 45

give 6 conservation techniques

Answer 45

international cooperation gene banks legislation ecotourism protecting habitats education

Question 46

describe international cooperation as a conservation technique

Answer 46

e.g. restricting trade in ivory or whaling

Question 47

explain gene banks as a conservation technique

Answer 47

conservation of existing gene pools involves: breeding programmes in zoos and botanic gardens re-introduction of species e.g. red kites sperm banks seed banks

Question 48

explain legislation as a conservation technique

Answer 48

national and international laws protecting habitats and wildlife e.g. EU habitats directive preventing overfishing by imposing fishing quotas, preventing overgrazing

Question 49

explain ecotourism as a conservation technique

Answer 49

aims to minimise the negative impacts of tourism by: contributing to conservation employing local people educating visitors cooperating with local people to manage areas

Question 50

explain protecting habitats as a conservation technique

Answer 50

protecting a particular area e.g. from urban development this includes National Parks, site of special scientific interest (SSSI) e.g. Dunham park

Question 51

explain education as a conservation technique

Answer 51

public awareness campaigns on global or national scales e.g. WWF, Countryside commission

Question 52

why is conservation of existing gene pools important and explain each?

Answer 52

ethical reasons: each species is a unique combination of genes and alleles and so is therefore valuable agriculture and horticulture: breeds of animals and plants used in agriculture and horticulture have been selectively bred so may lack rare alleles that could be important in the future e.g. disease resistance wild plants and animals can act as a gene bank for these alleles which animals and crop plants can be bred with environmental change: a large, varied gene pool increases the chance of a species surviving environmental change potential medical uses: plants and animals may have the potential to help in the development of new drugs or other medical treatments, bu preserving habitats we allow this potential to be researched in the future

Question 53

describe re-introduction of species

Answer 53

reintroduction of an organism to its native habitat, an area from which it has been previously lost reintroduction aims to re-establish a viable population of the species within its native habitat and can be a positive conservation strategy e.g. introduction of beavers into uk, wolves in Yellowstone national park, siberian tiger introduction project

Question 54

define keystone species

Answer 54

a species with a dramatically large effect on an ecosystem relative to its abundance e.g. mountain lion (page 14)

Question 55

what factors must scientists consider is this reintroduction is to be successful and explain each?

Answer 55

habitat: the receiving habitat is suitable, the effect of species introduction on habitat or effect on biodiversity research: the resources and expertise are available for the establishment and protection of the reintroduced species consultation: this would occur between neighbouring landowners and local stakeholders, to make sure that the majority of those consulted do not oppose reintroduction correct individuals: a suitable disease-free donor population is identified, and the correct species os reintroduced

Question 56

why can reintroduction into areas where there are no well-established populations help?

Answer 56

there are fewer predators less intraspecific competition for food/nest sites/habitats less likely to pass on diseases as fewer numbers (initially)

Question 57

why could illegal or unregulated reintroduction be a concern?

Answer 57

introduction of disease e.g. TB in beavers destruction or loss of habitats and other effects on ecosystem the wrong species would not be so well adapted

Question 58

give three farming methods with wide environmental implications

Answer 58

removal of hedgerows to make larger fields monoculture overgrazing

Question 59

explain removal of hedgerows to make larger fields

Answer 59

this allows farmers to use larger machinery to plough the soil and harvest crops reduces biodiversity by removing breeding sites, feeding sites and wildlife 'corridors' which allow animals to move from one area to another

Question 60

explain monoculture

Answer 60

single crops e.g. maize, wheat, barley are grown in large fields this will have an effect on biodiversity as it only provides one habitat, reducing the number of different microhabitats that would be available in an area with mixed crops roots grow to same length and extract the same minerals from the same depth of soil, reducing the concentrations of nutrients in the soil and increasing the use of inorganic fertilisers

Question 61

explain overgrazing

Answer 61

overgrazing occurs when plants are exposed to intensive grazing for extended periods of time overgrazing can lead to soil erosion and desertification hooves of cattle compact soil, driving out air and preventing water drainage roots cannot penetrate the soil and grass for grazing cannot grow

Question 62

what are the reasons for deforestation? (6)

Answer 62

demand for timber as a construction material wood used for fuel to make paper and cardboard packaging to clear the land for farming to improve transport infrastructure by building new roads targeting high value trees e.g. teak and mahogany

Question 63

give three consequences of deforestation

Answer 63

global climate change destruction of habitats soil erosion

Question 64

explain global climate change as a consequence for deforestation

Answer 64

if trees are cut down less carbon dioxide is removed from the atmosphere by photosynthesis felled trees will also increase the concentration of carbon dioxide in the atmosphere because: combustion of trees releases carbon dioxide from biomass logs decompose and decomposers release CO2 fossil fuels burnt in transport of logs

Question 65

what effect will destruction of habitats have on biodiversity and why is this a particular issue in tropical rainforests?

Answer 65

reduces biodiversity since 50% of Earth's species live in rainforests which damages global biodiversity and rainforests might have plants that have undiscovered medical properties

Question 66

describes soil erosion

Answer 66

the removal of top soil which contains valuable nutrients removal of trees on higher sloes can lead to lowland flooding after heavy rainfall the topsoil in the sloped areas can also be swept away by the rain

Question 67

why is there an increase in soil erosion if trees are removed from an area?

Answer 67

there are no roots to hold soil so it can easily wash away

Question 68

why isn removal of top soil a particular problem?

Answer 68

top soil is fertile (high nutrient content) the soil below is not suitable for crop growth

Question 69

give 4 results of deforestation

Answer 69

evaporation vs transpiration decreased oxygen in soil soil temperature reduced denitrifying bacteria

Question 70

explain evaporation vs transpiration

Answer 70

evaporation from soil returns water more slowly to the atmosphere than transpiration does, leading to reduced local rainfall and accelerated desertification

Question 71

explain decreased oxygen in soil

Answer 71

as the soil becomes wetter water fills the soil's airspaces and the oxygen available for roots decreases

Question 72

explain soil temperature being reduced

Answer 72

it takes wet soil longer to warm up than dry soil, meaning these soils are cold this reduces germination and root activity

Question 73

explain denitrifying bacteria

Answer 73

cold, damp soil favours the growth of denitrifying bacteria so soils lose inorganic nitrogen compounds and so is less' fertile'

Question 74

describe forest managment

Answer 74

it is the sustainable replanting and regeneration of forests with careful management it is possible to remove timber without destroying the forest ecosystem, especially if only a small number of trees are removed each year, leaving the habitat intact

Question 75

give other five techniques of managing forests

Answer 75

coppicing selective cutting long rotation times planting trees optimum distances apart controlling pests and diseases

Question 76

explain coppicing

Answer 76

a tree trunk is cut but a 'stool' a few cm high is left new shoots emerge from the stool and grow into 'poles' the poles can be cut on rotation to produce timber of different widths coppiced plants can regenerate over long periods of time

Question 77

explain selective cutting

Answer 77

some of the larger trees are felled whilst others are left in place it is this particularly useful on steep slopes and near rivers because on steep slopes the total removal of trees would leave the soil vulnerable to soil erosion and selective cutting helps maintain nutrients in the forest soil and minimise the amount of soil which is washed into rivers and other waterways

Question 78

explain long rotation times

Answer 78

letting trees grow for a long period of time before cutting them down

Question 79

what effect will a long rotation time have on the habitat diversity and associated biodiversity of an area?

Answer 79

increases habitat/area diversity as it provides more stable, long term habitats

Question 80

explain planting trees optimum distances apart

Answer 80

reduces intraspecific competition which can lead to trees growing tall and thin and so producing poor quality timber

Question 81

explain controlling pests and diseases

Answer 81

ensures trees grow well and produce high quality timber, then then means that fewer trees need to be felled and the bet use is made of the land

Question 82

why is it important that native woodlands are preserved?

Answer 82

maintain and enhance biodiversity by ensuring there is a wide range of habitats available

Question 83

describe overfishing

Answer 83

it is a problem because increased intensity and efficiency of modern fishing is having a highly negative effect on the populations of some marine organisms using small mesh sizes means smaller, juvenile fish which are not sexually mature are unable to escape nets this reduces the future breeding population; over time this leads to fewer offspring and reduces genetic diversity

Question 84

what are the effects of overfishing on other wildlife?

Answer 84

drift nets can catch non-target species such as turtles or dolphins trawling damages the sea floor habitat of organisms such as some molluscs e.g. clams can catch organisms that are the prey of other species e.g. catching capelin which is eaten by cod or krill, which is eaten by some whales, seals, penguins, squid and fish... it can affect whole food webs

Question 85

what controls can be used to reduce the impact of overfishing?

Answer 85

impose quotas on catches so only a certain mass of fish can be landed ensure mesh sizes of nets are large enough to let young fish escape enforcement of exclusion zones legislate size of fishing fleets and number of days at sea encourage consumers to eat sustainably sourced fish

Question 86

what additional problems can imposing quotas on catches so only a certain mass of fish can be landed lead to?

Answer 86

excess fish are still caught and killed, but those over quota are disregarded (wasteful)

Question 87

why is ensuring mesh sizes are large enough to let young fish escape important?

Answer 87

young fish can escape nets so they can grow and become sexually mature and then reproduce

Question 88

what areas and at what times of year should fishing boats be unable to fish?

Answer 88

in areas where fish breed (breeding grounds) during (spawning) the breeding season

Question 89

what is fish farming used for?

Answer 89

species like salmon and trout in the uk

Question 90

describe fish farming

Answer 90

fish are bred and grown to maturity in enclosures in ponds, lakes, estuaries or in tanks on land it can be used to overcome problem of overfishing but causes other problems too

Question 91

give advantages of farming fish rather than traditional livestock

Answer 91

fish convert their food into protein more efficiently a greater proportion of a fish's body is edible fish farming has a lower carbon footprint

Question 92

give 4 fish farming problems

Answer 92

diseased fish pollution resource use environmental toxins environmental degradation

Question 93

explain the problem of diseased fish in fish farming

Answer 93

salmon farms often have a high density so can easily transmit disease large amounts of antibiotics and pesticides have to be used to keep the fish healthy the pesticides used can harm other organism such as marine invertebrates escaped fish can also pass parasites and other infections to wild populations

Question 94

explain the problem of pollution in fish farming

Answer 94

effects the ecological balance of waterways, waste from fish farms can get into water around the fish pens and lead to eutrophication

Question 95

explain the problem of resource use in fish farming

Answer 95

farmed fish can eat a large amount of food, which is often other fish, this is inefficient

Question 96

explain the problem of environmental toxins in fish farming

Answer 96

environmental toxins e.g. PCBs and pesticides are more concentrated in farmed fish than in wild fish

Question 97

explain the problem of environmental degradation in fish farming

Answer 97

local environment can be damaged e.g. shrimp industry leading to salinisation of soil and groundwater leading to destruction of mangroves

Question 98

describe and define planetary boundaries

Answer 98

they were designed to define a 'safe operating space for humanity' scientists believe that once human activity has passed certain thresholds (planetary boundaries), there is a risk of 'irreversible and abrupt environmental change'

Question 99

give the 9 planetary boundaries

Answer 99

biodiversity boundary climate change nitrogen land use fresh water ocean acidification ozone chemical pollution aerosol

Question 100

has the biodiversity boundary been crossed?

Answer 100

yes

Question 101

explain the concept of the biodiversity boundary in relation to human activities

Answer 101

human activity has caused environmental changes to happen too fast for natural selection to produce organisms that are adapted to this changing environment as a result, many species have become extinct habitat change in regions such as tundra (temperature rises) and marine environments (pollution of oceans with acid, oil and sewage) this has caused concern and biodiversity has been significantly reduced in these regions coral reef bleaching and coastal plain submersion due to rising sea levels are also reducing biodiversity

Question 102

what can we do to help the biodiversity boundary?

Answer 102

monitoring biodiversity, collecting materials for gene banks, raising public awareness to reduce human behaviour that has generated biodiversity loss

Question 103

explain the concept of the climate change boundary in relation to human activities and has it been crossed?

Answer 103

greenhouse gases are continually being added to the atmosphere this is causing an increase in global temperature, climate change, rise in sea levels yes its been crossed

Question 104

what can we do to help the climate change boundary?

Answer 104

the production of biofuels which are made by biological processes as the growth of biofuel crops takes in carbon dioxide from the atmosphere, the release of carbon dioxide when they're burnt has less impact - carbon neutral biofuels can be made by anaerobic digestion of plant material

Question 105

explain the concept of the nitrogen boundary in relation to human activities and has it been crossed?

Answer 105

denitrification due to waterlogged soils use of agricultural fertilisers leading to eutrophication yes - been crossed

Question 106

what can we do to help the nitrogen boundary?

Answer 106

planting fields of legumes to increase nitrogen fixation ploughing soil to improve aeration and prevent anaerobic conditions

Question 107

explain the concept of the land use boundary in relation to human activities and has it been crossed?

Answer 107

deforestation to allow for farming and urban development has led to a conflict between the need to grow food and the need to grow biofuels and protect natural habitats yes - been crossed

Question 108

what can we do to help the land use boundary?

Answer 108

changing farming practises to concentrate it in the most productive areas reducing consumption of meat would reduce land being cultivated

Question 109

explain the concept of the fresh water boundary in relation to human activities

Answer 109

it is unavoidable many organisms must have access to fresh water to live the fresh water boundary would be crossed if organisms do not have enough fresh water to survive only 2.5% of water on Earth is fresh water, it is important as it only contains a low concentration of dissolved salts the decrease in supply of freshwater is due to changing landscapes, agriculture, increased demand from humans, water pollution and climate change

Question 110

what can we do to help the fresh water boundary?

Answer 110

water conservation (not irrigating non-food crops), water efficiency, waste water reclamation and drip irrigation systems desalination is an important technology that removes minerals from salt water to produce fresh water

Question 111

explain the concept of the ocean acidification boundary in relation to human activities

Answer 111

it is unavoidable the pH of the oceans is decreasing due to dissolving carbon dioxide forming carbonic acid which releases hydrogen ions low pH leads to mollusc, coral shells and arthropod exoskeletons softening making them vulnerable gill structure in fish is also affected by low pH and their functioning is damaged

Question 112

what can we do to help the ocean acidification boundary?

Answer 112

reduction in the burning of fossil fuels

Question 113

explain the concept of the ozone boundary in relation to human activities

Answer 113

chloro-fluorocarbons (CFCs) favour the breakdown of the ozone CFCs were widely used in spray cans, solvents, refrigerator coolants and manufacture of food and drink containers this resulted in the thinning and development of a 'hole' in the ozone layer the use of CFCs in spray cans was banned in 1978 the ozone layer is now recovering naturally it has been avoided

Question 114

explain the concept of the chemical pollution boundary in relation to human activities

Answer 114

it is unquantified (so variable that a boundary hasn't been suggested) organic pollutants, radioactive materials, nano-materials and micro-plastics these could all interact with each other and produce harmful effects

Question 115

explain the concept of the aerosol boundary in relation to human activities

Answer 115

it is unquantified atmospheric aerosols are the microscopic particles put into the atmosphere by combustion of fuels and by creating dust from digging and quarrying these can lead to respiratory problems and cause death from lung disease sulphates in aerosols reflect sunlight, providing a cooling effect but other particulates reradiate it, increasing warming